With this beginner's code, I am trying to ask the user for input as long as the input is not 'quit'. My code:
void createReport(){
printf("Welcome to the report generator, type item's ID: ");
char *userInput;
int i=0;
struct myStruct{
char *name;
int id;
float sale;
};
struct myStruct *myStructArray[MAX_ITEMS];
fgets(userInput,sizeof(int),stdin);
while(strcmp(userInput,"quit")!=0) {
userInput = malloc(sizeof(int));
fgets(userInput,sizeof(int),stdin);
searchA(userInput); //different function that changes global variable deletion
printf("Added to the report, add more or type \'quit\' \n");
strcpy(myStructArray[i]->name,inventoryItem[deletion].name); //inventoryItem is global
myStructArray[i]->id = atoi(input);
myStructArray[i]->sale = inventoryItem[deletion].sale;
i++;
free(userInput);
}
for(int x=0;x<30;x++) printf(myStructArray[x]->name); //never executed
}
This code runs once, asking the user for input, and then finishes
Does anybody know where can be the mistake? Thanks for any suggestions
Before the while loop you do
fgets(userInput,sizeof(int),stdin);
at that moment your variable userInput is not yet to be set.
Edit:
Running example of the idea of the code:
printf("Welcome to the report generator, type item's ID: ");
const int input_size = 6 * sizeof(char);
char *userInput = malloc(input_size);
int i = 0;
struct myStruct {
char *name;
int id;
float sale;
};
struct myStruct *myStructArray[MAX_ITEMS];
fgets(userInput, input_size, stdin);
while (strcmp(userInput, "quit") != 0 && strcmp(userInput, "quit\n") != 0)
{
// do whatever you like with myStructArray[i], for example:
myStructArray[i] = malloc(sizeof(struct myStruct));
myStructArray[i]->name = malloc(sizeof(char));
myStructArray[i]->name = "ab";
myStructArray[i]->id = 7;
myStructArray[i]->sale = 99.9F;
printf("Added %s, %d, %f\n", myStructArray[i]->name, myStructArray[i]->id, myStructArray[i]->sale);
//prepare for next iteration:
printf("Added to the report, add more or type \'quit\' \n");
for (int j = 0; j < input_size; ++j) // zeroing allocated data on the heap
userInput[j] = 0;
fgets(userInput, input_size, stdin);
i++;
}
free(userInput);
for (int x = 0; x < i; x++) printf("%s,", myStructArray[x]->name);
Related
I have made one program, where you enter a few characters (10 max). It makes you a list, count average length of surnames, tell about how much different names. But the problem is, when I enter the last number (10) - it sorts me it incorrectly (like 39399349349, 3443993). Beneath I will present my code. I am newbie in C, so please don't shut on me) I am convinced that sorting function is incorrect, but don't know what exactly(
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct people {
int num[10];
char surname[20];
char name[10];
} peoples[10], c;
int compare_people_num(const void *a, const void *b);
int main()
{
int i, j, k = 0, l = 0, m = 0, n = 0;
float s = 0;
char str[100];
system("chcp 1251 > nul");
for (i = 0, j = 0; i < 10; i++, j++)
{
printf("Enter number, surname, name %d of your human: ", i + 1);
fgets(str, sizeof str, stdin);
sscanf(str, "%d %s %s", &peoples[j].num, &peoples[j].name, &peoples[j].name);
while (str[n] != '\n')
{
if (str[n] != ' ')
{
peoples[j].num[k] = str[n];
}
else
break;
n++;
k++;
}
n++;
k = 0;
while (str[n] != '\n')
{
if (str[n] != ' ')
{
peoples[j].surname[k] = str[n];
}
else
break;
n++;
k++;
}
n++;
k = 0;
while (str[n] != '\n')
{
if (str[n] != '\0')
{
peoples[j].name[k] = str[n];
}
else
break;
n++;
k++;
}
n = 0;
k = 0;
}
for (i = 0; i < 10; i++)
{
for (j = i + 1; j < 10; j++)
{
if (!strcmp(peoples[i].name, peoples[j].name))
m = 1;
}
if (m == 0)
l++;
m = 0;
s = s + strlen(peoples[i].surname);
}
for (i = 0; i < 9; i++)
for (j = 0; j < 9; j++)
if (strcmp(peoples[j].num, peoples[j+1].num) > 0)
{
qsort(peoples, 10, sizeof(struct people), &compare_people_num);
}
for (i = 0; i < 10; i++)
{
printf("%d ", peoples[i].num);
printf("%s ", peoples[i].name);
printf("%s ", peoples[i].surname);
printf("\n");
}
printf("\nYou have %d different names\n", l);
printf("Avarege lenght of surname is = %f\n", s / 10);
}
int compare_people_num(const void *a, const void *b)
{
const struct people *p1 = a;
const struct people *p2 = b;
return p1->num - p2->num; // Change order to reverse sort
}
I went through your code and removed things that weren't needed. In both your input and sorting, it seemed like you were doing things twice. I tried to document the changes I made and explain why they should be made.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// It's generally a good idea to use #define when you have some global constants
// I made some of the constants larger than what you showed to prevent issues
#define MAX_NAME_LEN 40
#define MAX_SURNAME_LEN 40
#define NUM_PEOPLE 10
#define BUFF_LEN 100
// Separate your struct...
struct person {
int num;
char name[MAX_NAME_LEN];
char surname [MAX_SURNAME_LEN];
};
// ... and array decleration
static struct person people[NUM_PEOPLE];
// I added this function, to make it easier to display a person
void print_person (const struct person * p) {
printf("Person %d %s %s\n", p->num, p->name, p->surname);
}
// This function will print out every person in the people array
void print_people (void) {
for (int i=0; i<NUM_PEOPLE; i++) {
print_person(&people[i]);
}
}
// Compares two people by number
int compare_people_num (const void * a, const void * b) {
struct person * p0 = (struct person *) a;
struct person * p1 = (struct person *) b;
return p0->num - p1->num;
}
// Compares two people by name
int compare_people_name (const void * a, const void * b) {
struct person * p0 = (struct person *) a;
struct person * p1 = (struct person *) b;
return strcmp(p0->name, p1->name);
}
int main (void) {
int i;
char buffer[BUFF_LEN];
for (i=0; i<NUM_PEOPLE; i++) {
printf("Enter number, surname, and name of person %d: ", i+1);
fflush(stdout); // fflush makes sure that our text is shown to the user
fgets(buffer, BUFF_LEN, stdin); // Read user input in to buffer
// It's unclear what you were doing here
// This sscanf line takes a line of text, and splits it into a number and two words
// It then stores that number in people[i].num, and stores the words in name and surname
// However, right after this, you have several while loops that appear to be manually doing the same
// thing all over again. If you want to read all of the input in, just the line below is enough
sscanf(buffer, "%d %s %s", &people[i].num, people[i].name, people[i].surname);
}
// We've read all of the people in now
// Uncomment the next line to check out the output at this state:
// print_people();
// To count names, we first need to sort the people by their name
// We do this using a qsort call
qsort(people, NUM_PEOPLE, sizeof(struct person), compare_people_name);
// Once the names are sorted, we'll calculate how many different names there are
// We start the count at 1, and start checking from the second person (index 1)
// This is because the first person will always be unqiue, and we can't compare to
// person negative 1
int n_names = 1;
for (i=1; i<NUM_PEOPLE; i++) {
char * current = people[i].name;
char * previous = people[i-1].name;
if (!strcmp(current, previous)) {
n_names ++;
}
}
// Now we have to sort the people based on their num field
// Again, in your code, it looked like you were doing this more than nessecary
// We just have to call qsort once, as such
qsort(people, NUM_PEOPLE, sizeof(struct person), compare_people_num);
// We will also do a loop through to calculate the average surname length
float avg_surname_len = 0;
for (i=0; i<NUM_PEOPLE; i++) {
avg_surname_len += (float)strlen(people[i].surname);
}
avg_surname_len /= (float)NUM_PEOPLE;
// We're all done! The people are sorted by number.
print_people();
printf("There are %d unique names\n", n_names);
printf("The average surnames is %f characters\n", avg_surname_len);
}
I created a struct of student inside the function using malloc and populated it with data. I want to return the address of the array of struct back to main and print it line by line, but with my implementation, it is not printing. I debugged my code and indeed, it is able to return the address of my array to main. I don't know why it's not printing though. Any thoughts?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct student Student;
struct student
{
char name[100];
int age;
char sex;
};
Student **getstudents(int n)
{
Student **t = malloc(sizeof *t * n); // memory for the array of pointers
for (int i = 0; i < n; i++) // memory for each individual pointer
{
t[i] = malloc(sizeof **t);
}
/* Data is inputted by user with form <student> <sex> <age>, then get mapped to the struct *t */
return t; /* Pointer to an array of pointers */
}
int main()
{
Student **students;
int n;
scanf("%d\n", &n);
students = getstudents(n);
for (int i = 0; i < n; i++)
{
printf("Name: %s, Sex: %s, Age: %d\n", students[i]->name, students[i]->sex, students[i]->age);
}
for (int i = 0; i < n; i++)
{
free(students[i]);
}
free(students);
return 0;
}
I am only allowed to modify the code in `Student **getstudents(int n)`.
In the line:
Student *t = (char*)malloc(sizeof(Student)*n);
You are allocating memory for one pointer, if you want to return a pointer to pointer, you need to allocate memory accordingly:
Student **t = malloc(sizeof *t * n); // memory for the array of pointers
for(int i = 0; i < n; i++){ // memory for each individual pointer
t[i] = malloc(sizeof **t);
}
To later free the pointers you also need to free each individual pointer previously allocated:
for(int i = 0; i < n; i++){ // memory for each individual pointer
free(students[i]);
}
free(students);
Note that the specifier for a single character is %c, the printf will need to be corrected:
printf("Name: %s, Sex: %c, Age: %d\n", students[i]->name, students[i]->sex, students[i]->age);
// ^^
Another thing I would change is in strncpy instead of null terminating the string later I would let the function do it:
// one more byte and strncpy terminates the string for you
strncpy(t[i]->name, data[0], strlen(data[0]) + 1);
// ^^^^
// already corrected for the new pointer
Having corrected the issues here is a possible alternative you can use to parse all the elements in the struct with sscanf from entry in one go, if you want to:
Student **getstudents(int n)
{
Student **t = malloc(sizeof *t * n); // memory for the array of pointers
if (t == NULL)
{
perror("malloc");
exit(EXIT_FAILURE);
}
for (int i = 0; i < n; i++) // memory for each individual pointer
{
t[i] = malloc(sizeof **t);
if (t[i] == NULL)
{
perror("malloc");
exit(EXIT_FAILURE);
}
}
for (int i = 0; i < n; i++)
{
char entry[100];
if (fgets(entry, sizeof entry, stdin))
{
if (sscanf(entry, "%25s %c %d", t[i]->name, &t[i]->sex, &t[i]->age) != 3)
{
// deal with bad input
}
}
}
return t;
}
anastaciu answer points many troubles, but there is others :
Another problem in your code is that you use '%s' for the sex as sex is a only char. You should use %c or else the printf function will try to parse a string and will get a SEGFAULT.
I urge you too to stricly check every memory allocation. Always.
The revised code from my pov :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct student Student;
struct student{
char name[100];
int age;
char sex;
};
Student **getstudents(int);
void free_students(Student**, int);
int main(){
Student **students;
int n = 4;
students = getstudents(n);
for(int i = 0; i < n; i++){
if (students[i] != NULL) {
printf("Name: %s, Sex: %c, Age: %d\n", students[i]->name, students[i]->sex, students[i]->age);
}
}
free_students(students, n);
return 0;
}
Student **getstudents(int n){
Student **t = (Student **)malloc(sizeof(Student *)*n);
if (t==NULL) {
perror("Memory: can't allocate.");
return(NULL);
}
/* Input: <name> <sex> <age> */
char entry[100];
for(int i = 0; i < n; i++){
t[i]=NULL;
if (fgets(entry,100,stdin) != NULL) {
int readBytes = strlen(entry);
char newString[3][25];
int k,j,ctr;
j=0; ctr=0;
for(k=0;k<=readBytes;k++)
{
if(entry[k]==' '||entry[k]=='\0'||entry[k]=='\n')
{
newString[ctr][j]='\0';
ctr++;
j=0;
}
else
{
newString[ctr][j]=entry[k];
j++;
}
}
t[i] = (Student *)malloc(sizeof(Student));
if (t[i] == NULL) {
perror("Memory: can't allocate.");
return(NULL);
}
strncpy(t[i]->name, newString[0], strlen(newString[0]));
t[i]->name[strlen(newString[0])] = '\0';
t[i]->sex = *newString[1];
t[i]->age = atoi(newString[2]);
}
}
return t;
}
void free_students(Student **students, int n){
for(int i=0; i<n; i++){
free(students[i]);
}
free(students);
}
I am trying to create a database program of students where you should be able to add/modify and delete students. I have managed to get the add function working, and also the modify function but the delete function gives me some problems. my code seems to crash when im trying to delete a student from the database, can anyone tell me where the problem lies?
Here's my code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* TODO: Avoid global variables. */
struct student {
char name[60];
long long personalNumber;
char gender[6];
char studyProgram[60];
char email[30];
int age;
};
struct student *pointer = NULL;
int numberofstudents = 0;
void modify()
{
long long persnr;
long long comp;
int match = 0;
printf("Please enter the personal number that you wish to modify: \n");
scanf("%lld", &persnr);
getchar();
for(int i = 0; i <= numberofstudents; i++)
{
comp = ((pointer+i)->personalNumber);
printf("%lld\n", ((pointer+i)->personalNumber));
printf("%lld\n", comp);
printf("Inne");
if (pointer[i].personalNumber == persnr && match == 0)
{
printf("Enter name, personalnumber, gender, studyprogram, email and age in this order\n");
scanf("%s%lld%s%s%s%d", (pointer+i)->name, &(pointer+i)->personalNumber, (pointer+i)->gender, (pointer+i)->studyProgram, (pointer+i)->email, &(pointer+i)->age);
match = 1;
getchar();
}
if (match == 0)
{
printf("Could not find person");
}
}
}
void deletestudent()
{
long long persnr;
long long comp;
int match = 0;
printf("Please enter the personal number that you wish to delete: \n");
scanf("%lld", &persnr);
getchar();
struct student *temporary = malloc((numberofstudents - 1) * sizeof(struct student));
for(int i = 0; i <= numberofstudents; i++)
{
if (pointer[i].personalNumber == persnr && match == 0)
{
match = 1;
}
else if (match == 1){
temporary[i-1] = pointer[i];
}
else
{
temporary[i] = pointer[i];
}
if (match == 0)
{
printf("Could not find person");
}
}
free(pointer);
pointer = temporary;
}
void add(){
if (numberofstudents > 0)
{
pointer = (struct student*) realloc(pointer, (numberofstudents+1) * sizeof(struct student));
printf("Lyckades allokeringen!\n\n");
}
printf("Enter name, personalnumber, gender, studyprogram, email and age in this order\n");
scanf("%s%lld%s%s%s%d", (pointer+numberofstudents)->name, &(pointer+numberofstudents)->personalNumber, (pointer+numberofstudents)->gender, (pointer+numberofstudents)->studyProgram, (pointer+numberofstudents)->email, &(pointer+numberofstudents)->age);
getchar();
printf("Visar data:\n");
for(int i = 0; i <= numberofstudents; ++i)
{
printf("%s\t%lld\t%s\t%s\t%s\t%d\n", (pointer+i)->name, (pointer+i)->personalNumber, (pointer+i)->gender, (pointer+i)->studyProgram, (pointer+i)->email, (pointer+i)->age);
}
numberofstudents = numberofstudents+1;
}
int main(void)
{
pointer = (struct student*) malloc(2 * sizeof(struct student));
if (pointer == NULL)
{
printf("pointer NULL");
exit(1);
}
int run = 1;
int choice;
while (run == 1)
{
printf("Please enter an option listed below\n1.ADD\n2.Modify\n3.Delete\n4.Search\n5.Save\n6.Load\n7.Exit");
scanf("%d", &choice);
getchar();
switch(choice) {
case 1 :
add();
break;
case 2 :
modify();
break;
case 3 :
deletestudent();
case 7 :
exit(0);
break;
default :
break;
}
}
return 0;
}
As mentioned in a comment, this:
for(int i = 0; i <= numberofstudents; i++)
is a huge warning sign. In C, such a loop should typically have i < numberofstudents in it, assuming numberofstudents is the actual length of the array.
Using <= rather than < makes the loop go one step too far, thus indexing outside the array and causing undefined behavior.
Writing outside heap-allocated memory and then trying to free() it is a good way to provoke crashes, since there's a chance you're stepping on the heap allocator's data structures (in practice; in theory all that happens is that you get undefined behavior and thus anything can happen).
I am currently creating a really simple program for my beginners course in C programming and I am stuck. I want to be able to print the 5 best scores that are saved in a text file but right now it is only showing the first 5 lines not the best scored lines. The history part works okay and is printing everything but I cannot understand how to print the 5 best scores, maybe it has to do with sorting out the information in the extern text file? Sorry if this post is dumb but I need to ask somewhere (I am really basic at this).
Here is a part of the code that I think is not working properly, it is for codeblocks:
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
char name [40]; // Here every integer and character etc. is introduced as global.
int menu(char *name);
int startPractice(int choice);
int startTest(int choice, char *name);
char randomOperator();
int getRandomNumber(int min, int max);
int calc(int a, int b, char c);
int rand(void);
int showHistory();
int saveHistory(char *name, float average);
int showTop5();
struct gamer{
char *username;
float average;
};
int main()
{
printf("Hello and welcome to the program!\n"); // This is the introduction
printf("\nWhat is your name? ");
scanf("%s", &name);
printf("\nWelcome %s! \n\nWhat would you like to do? \n" , name);
menu(&name); // This line calls the main menu.
return 0;
}
int compare(const void *s1, const void *s2)
{
struct gamer *g1 = (struct gamer *)s1;
struct gamer *g2 = (struct gamer *)s2;/* same gender so sort by id */
return g1->average - g2->average;
}
int menu(char *name) { // This is the main menu and whenever this function is called the program starts from here.
int qanswer; // This variable is set so it can be used in this body, it is not a global integer.
printf("\n1. Do practices \n2. Do a test \n3. Quit \n4. Test history \n5. Top 5 \n");
scanf("%d", &qanswer);
switch (qanswer) { // Switch cases for a more compressed code, here only one case will be activated and that is decided by the value of "qanswer".
case 1:
printf("\nNow, you can choose to do practices on: \n\n1. Additions\n2. Subtractions\n3. Addition and Subtractions: ");
printf("\n\nEnter your choice: ");
scanf("%d" , &qanswer);
startPractice(qanswer);
break; //This breaks the code at any chosen case.
case 2:
printf("\nYou will be given 15 questions to solve as the test!\n\n");
printf("\nYou can choose to do the test on: \n\n1. Additions\n2. Subtractions\n3. Addition and Subtractions: ");
printf("\n\nEnter your choice: ");
scanf("%d", &qanswer);
startTest(qanswer, name);
break;
case 3:
printf("\nExiting program... \n");
exit(0); // Shuts down the program.
break;
case 4:
printf("Test history\n");
showHistory();
break;
case 5:
printf("Top 5 test results:\n");
showTop5();
break;
default: // if the user enter anything except 1,2,3 this line of code will be returned.
printf("Your input wasn't valid. Please try again...\n\n");
menu(name); // This calls the main menu again
}
return 0;
}
int startPractice(int choice) { // If practice is chosen then this function will be called.
int a, b, answer1;
char c;
int i;
for (i = 1; i <= 10; i++) { // The for loop runs this code until i=10 and increases by 1 each time. Therefore this code will run 10 times fully.
a = getRandomNumber(1, 30); // This calls the function for a random number.
b = getRandomNumber(1, 30);
if (choice == 1) { // If choice is set to "1" c will be t to + otherwise -.
c = '+';
} else if (choice == 2) {
c = '-';
} else {
c = randomOperator();
}
printf("%d. %d %c %d = ", i, a, c, b);
scanf("%d", &answer1);
while (answer1 != calc(a, b, c)){
printf("Try again! ");
scanf("%d", &answer1);
}
printf("Very good!\n\n");
}
printf("Practice is complete\n");
printf("\nNow what would you like to do?\n");
menu(name);
return 0;
}
int startTest(int choice, char *name) {
int a, b, answer1;
char c;
int counter = 0;
float average;
int i;
for (i = 1; i <= 15; i++) {
a = getRandomNumber(1, 30);
b = getRandomNumber(1, 30);
if (choice == 1) {
c = '+';
} else if (choice == 2) {
c = '-';
} else {
c = randomOperator();
}
printf("%d. %d %c %d = ", i, a, c, b);
scanf("%d", &answer1);
if (answer1 == calc(a, b, c)){
counter++;
}
printf("\n\n");
}
printf("The test is complete\n");
average = (float) counter/(float)15; // This calculates the average score as a float with the counter / 15.
printf("You scored %d out of 15 which is and average of %d %%\n", counter, (int)average*100); // This line takes the value of average and multiply it by 100 to show the percentage.
saveHistory("Test", average);
printf("\nNow what would you like to do?\n");
menu(name); // This function calls the main menu again.
return 0;
}
int calc(int a, int b, char c) { // This function is used to define the equation as (a + b) or (a - b).
switch(c) {
case '+':
return a+b;
case '-':
return a-b;
}
}
char randomOperator() { //This code is used to decide if + or - is going to be used.
switch(getRandomNumber(0,1)) { //Switch statement when you need two or more ways to return a value.
case 0:
return '+'; //If the random number is 0 return is + otherwise it is -.
case 1:
return '-';
}
return '+';
}
int getRandomNumber(int min, int max) { // This simply decides a random value of min 0 and max 1.
return rand() % (max + 1 - min) + min;
}
int showHistory(){
FILE *f;
char c;
f=fopen("test.txt","rt");
if (f) {
while((c=fgetc(f))!=EOF){
printf("%c",c);
}
fclose(f);
printf("\nWhat would you like to do now?\n");
} else {
printf("There is no history file at the moment.");
}
menu(name);
return 0;
}
int saveHistory(char *name, float average){
FILE *f;
char c;
f=fopen("test.txt","a");
fprintf(f, "%s_%.2f\n", name, average);
fclose(f);
return 0;
}
int showTop5(){
//printf("\n");
FILE *f;
char c;
char line[256];
int count = 0;
f=fopen("test.txt","rt");
if (f) {
while (fgets(line, sizeof(line), f)) {
if (strlen(line) > 0) {
count++;
}
}
char delimiter[] = "_";
char *ptr;
fclose(f);
f=fopen("test.txt","rt");
struct gamer gamers[count];
int i = 0;
printf("\n");
while (fgets(line, sizeof(line), f)) {
ptr = strtok(line, delimiter);
char n[40];
strcpy(n, ptr);
//printf("n: %s, ", n);
ptr = strtok(NULL, delimiter);
float avg = *(float *) ptr;
//printf("points: %f\n", avg);
gamers[i].average = avg;
gamers[i].username = n;
i++;
}
qsort(gamers, count, sizeof(struct gamer), compare);
int j;
for(j = 0; j < count; j++){
if (j==5){
break;
}
printf("Rank %d: %s with %.2f %% as average.\n", j+1, gamers[j].username, gamers[j]. average);
}
fclose(f);
} else {
printf("There is no history file at the moment.");
}
menu(name);
return 0;
}
This isnt going to work
ptr = strtok(NULL, delimiter);
float avg = *(float *) ptr;
you are treating the score in the file as though it were the binary representation of a float. It is not, it is text. You need to do
ptr = strtok(NULL, delimiter);
float avg = atof(ptr);
So when i fixed the code that made the program crash (as was mentioned in the answers, thanks!) it seems like the problem with the sorting came from this line of code not treating the values correct, since I wanted to return it as percentage and it must have stopped reading after the decimal which made every user either scoring 0 or 1 if this makes sense. It works now when the return value is multiplied by 100.
Started with this code:
int compare(const void *s1, const void *s2)
{
struct gamer *g1 = (struct gamer *)s1;
struct gamer *g2 = (struct gamer *)s2;/* same gender so sort by id */
return g1->average - g2->average;
}
And this code seems to be the problemsolver.
int compare(const void *s1, const void *s2)
{
struct Gamer *g1 = (struct Gamer *)s1;
struct Gamer *g2 = (struct Gamer *)s2;/* same gender so sort by id */
return (int)((g2->average - g1->average)*100);
After taking into account of previous remarks, it remains other problems before to manage correctly the sort of array of struct gamer by using the qsort() optimized function.
Problem 1 - no allocated space to store the username into a struct gamer.
The struct gamer is using a char *username;;
When reading data from "test.txt" file, the user name is storing only the pointer to the buffer instead of the content gamers[i]->username = n;;
Even if the read username is strcpy(n, ptr);, that storage is in the heap and be overwritten at the next reading operation;
As #pm100 suggestes, the average is decoded as a binary data instead of a text value float avg = *(float *) ptr;
In the showTop5() function use:
while (fgets(line, sizeof(line), f)) {
ptr = strtok(line, delimiter);
char n[40];
strcpy(n, ptr);
ptr = strtok(NULL, delimiter);
float avg = atof(ptr); // #pm100 proposed solution
gamers[i].average = avg;
gamers[i].username = (char *)malloc(sizeof(char)*(strlen(n)+1));
strcpy(gamers[i].username,n); // allocate and copy the username
i++;
}
Instead of
while (fgets(line, sizeof(line), f)) {
ptr = strtok(line, delimiter);
char n[40];
strcpy(n, ptr);
//printf("n: %s, ", n);
ptr = strtok(NULL, delimiter);
float avg = *(float *) ptr;
//printf("points: %f\n", avg);
gamers[i].average = avg;
gamers[i].username = n; // error no size allocated
i++;
}
Problem 2 - When using qsort() the structure of data shall have a fixed-size length. Use an array of pointer struct gamer * to be sorted.
If sizeof(struct gamer) is used to qsort(), the float average and the char *username will be sorted, but it is not optimized;
After allocating the size to store username, it will be not easy to free the memory if the array struct gamer gamers[count]; is allocated from the heap;
It the amount of gamers is large, storing in the heap could be a problem;
Allocating the gamers[] array:
struct gamer **gamers;
int i;
gamers = malloc(count*sizeof(struct gamer *));
for (i = 0; i < count; i++) {
gamers[i] = malloc(sizeof(struct gamer));
}
Manage the reading operation to the array:
See the source code in the Problem 1
Update the compare function of quicksort:
int compare(const void *s1, const void *s2)
{
struct gamer *g1 = *((struct gamer **)s1); // instead of (struct gamer *)s1;
struct gamer *g2 = *((struct gamer **)s2); // instead of (struct gamer *)s2;
// as #BeginnerC suggests, reverse the comparison
return ((int)((g2->average - g1->average)*100));
}
Perform the quicksort:
qsort(gamers, count, sizeof(struct gamer *), compare);
Print the Top 5 gamers:
for(j = 0; j < count; j++){
if (j==5){
break;
}
printf("Rank %d: %s with %.2f %% as average.\n", j+1,
gamers[j]->username, gamers[j]->average);
}
Free the allocated gamers[] array:
for (i = 0; i < count; i++) {
free (gamers[i]->username); // allocated to the username
free (gamers[i]);
}
free(gamers);
Note: in order to simplify the solution of Problem 1 and to have a fixed-size struct gamer, the field char *username could be replaced by char username[40]; (because char n[40]; before strcpy(n, ptr);.
Here's the part of my code:
Problem: It skips the input of "please enter your name" to "please enter your marks"
What I tried: flushall(); _flushall(); - which worked yesterday somehow, and trying to place these functions between printf,scanf..
student *Create_Class(int size) {
int i, j;
int idStud, nameStud, markStud;
student *classStudent;
classStudent = (student*)malloc(size * sizeof(student));
for (i = 0; i < size; i++) {
classStudent[i].name = (char*)malloc(51 * sizeof(char));
int numOfmarks = 4;
printf("Please enter your name: ");
gets(classStudent[i].name);
_flushall(); //tried _flushall() and it worked yesterday.. tried fflush(NULL) too.
printf("\nPlease enter 4 marks: ");
for (j = 0; j < numOfmarks; j++) {
scanf("%d", &classStudent[i].marks[j]);
}
Avg_Mark(&classStudent[i]);
}
return classStudent;
}
EDIT: (FULL CODE)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <conio.h>
typedef struct {
char *name;
int marks[4];
float avg;
} student;
student *Create_Class(int);
void Avg_Mark(student*);
void Print_One(student*);
void exStudents(student *s, int size);
int main() {
int size, i;
student *arr;
printf("\nEnter the number of students: \n");
scanf("%d", &size);
arr = Create_Class(size);
exStudents(arr, size);
for (i = 0; i < size; i++)
free(arr[i].name);
free(arr);
getch();
}
student *Create_Class(int size) {
int i, j;
int idStud, nameStud, markStud;
student *classStudent;
classStudent = (student*)malloc(size * sizeof(student));
for (i = 0; i < size; i++) {
classStudent[i].name = (char*)malloc(51 * sizeof(char));
int numOfmarks = 4;
int sizeOfName;
printf("Please enter your name: \n");
_flushall();
fgets(classStudent[i].name,50,stdin);
sizeOfName = strlen(classStudent[i].name);
printf("Please enter 4 marks: ");
for (j = 0; j < numOfmarks; j++) {
scanf("%d", &classStudent[i].marks[j]);
}
Avg_Mark(&classStudent[i]);
}
return classStudent;
}
void Avg_Mark(student *s) {
int i, numOfMarks = 4, sum = 0;
for (i = 0; i < numOfMarks; i++) {
sum += s->marks[i];
}
s->avg = (sum / 4.0);
}
void Print_One(student *s) {
printf("The average of %s is %f", s->name, s->avg);
}
void exStudents(student *s, int size) {
int flag = 1;
while (size > 0) {
if (s->avg > 85) {
Print_One(s);
flag = 0;
}
s++;
size--;
}
if (flag)
printf("\n There're no students with above 85 average.");
}
As you have already been told in comments, the solution is to use a two-step approach: Read lines first, then scan these lines as appropriate. This reflects how users are going to answer your prompts, namely by providing the information and then hitting enter.
Here's a variant of your code which does that. I've also changed the main function, because it also used scanf and I've added a function to strip white space from the string input by fgets. (This function requires the <ctype.h> header.)
#include <ctype.h>
int main()
{
char line[80];
int size, i;
puts("Enter the number of students:");
if (fgets(line, sizeof(line), stdin) == NULL) exit(1);
if (sscanf(line, "%d", &size) == 1 && size > 0) {
student *arr = Create_Class(size);
exStudents(arr, size);
for (i = 0; i < size; i++) free(arr[i].name);
free(arr);
}
return 0;
}
/*
* strip white space from beginning and end of string
*/
char *strip(char *str)
{
size_t l = strlen(str);
while (l > 0 && isspace((unsigned char) str[l - 1])) l--;
str[l] = '\0';
while (isspace((unsigned char) *str)) str++;
return str;
}
/*
* Create students and prompt user for input
*/
student *Create_Class(int size)
{
int i;
student *classStudent = malloc(size * sizeof(student));
for (i = 0; i < size; i++) {
char line[80];
char *p;
int okay = 0;
puts("Please enter your name:");
if (fgets(line, sizeof(line), stdin) == NULL) exit(1);
p = strip(line);
classStudent[i].name = malloc(strlen(p) + 1);
strcpy(classStudent[i].name, p);
while (!okay) {
int j = 0;
okay = 1;
puts("Please enter 4 marks:");
if (fgets(line, sizeof(line), stdin) == NULL) exit(1);
p = line;
while (p && j < 4) {
char *tail;
int m = strtol(p, &tail, 10);
if (p == tail) break;
if (m < 1 || m > 100) {
puts("Illegal mark.");
okay = 0;
}
classStudent[i].marks[j++] = m;
p = tail;
}
if (j < 4) {
printf("Expected 4 marks, but got %d.\n", j);
okay = 0;
}
}
Avg_Mark(&classStudent[i]);
}
return classStudent;
}
Please refrain from flushing buffers wihout reason. When a new-line character is written, stdout is flushed, so make it a rule to terminate all your strings with a new-line. New-lines at the beginning of strings instead of at the end are a sign of untidy output.
SOLUTION:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <conio.h>
typedef struct { //struct decleration
char *name;
int marks[4];
float avg;
} student;
//functions decleration
student *Create_Class(int);
void Avg_Mark(student*);
void Print_One(student*);
void exStudents(student *s, int size);
int main() {
/*variable declerations*/
int i, size;
char line[80];
student *arr;
/*Input number of students*/
printf("\nEnter the number of students: \n");
fgets(line, sizeof(line), stdin);
sscanf(line, "%d", &size);
/*Get name of students, marks, and calculate average above 85*/
arr = Create_Class(size);
exStudents(arr, size);
/*Free memory*/
for (i = 0; i < size; i++)
free(arr[i].name);
free(arr);
getch();
}
student *Create_Class(int size) { /*Get names of each student, and their 4 marks.*/
/*Variable declerations*/
int i, j;
char line[51];
student *classStudent;
/*Dynamic allocation to assign structure to every student*/
classStudent = (student*)malloc(size * sizeof(student));
/*Get name of students and their 4 marks*/
for (i = 0; i < size; i++) {
/*Variable decleration and dynamic allocation of 51 chars*/
classStudent[i].name = (char*)malloc(51 * sizeof(char));
int numOfmarks = 4;
int sizeOfName;
/*Input name of student*/
printf("Please enter your name: \n");
scanf("%s", classStudent[i].name);
/*Input marks of student*/
printf("Please enter 4 marks: ");
for (j = 0; j < numOfmarks; j++) {
scanf("%d", &classStudent[i].marks[j]);
}
/*Calculate average, and print averages of students above 85*/
Avg_Mark(&classStudent[i]);
}
return classStudent;
}
/*Calculate averages of students*/
void Avg_Mark(student *s) {
int i, numOfMarks = 4, sum = 0;
for (i = 0; i < numOfMarks; i++) {
sum += s->marks[i];
}
s->avg = (sum / 4.0);
}
/*Print average (if bigger than 85)*/
void Print_One(student *s) {
printf("The average of %s is %0.1f\n", s->name, s->avg);
}
/*Check whether the average is bigger than 85*/
void exStudents(student *s, int size) {
int flag = 1; //flag to check if there are any students with avg above 85
while (size > 0) {
if (s->avg > 85) {
Print_One(s); //Print the average
flag = 0; //We found atleast one student with avg > 85
}
s++; //Advance to next student
size--;
}
if (flag)
printf("\n There're no students with above 85 average.");
}
The problem in your code is that scanf does not consume the new-line returned by the user in:
scanf("%d", &size);
So when the program reaches:
fgets(classStudent[i].name,50,stdin);
the remaining new-line in stdin is received before the user can type anything.
A solution is to replace the initial scanf call by fgets and atoi calls.
char size_str[5];
fgets(size_str,5,stdin);
size = atoi(size_str);
A combination of fgets and sscanf also works also fine in general to first process user inputs and then convert it.
The variant with sscanf is:
char size_str[5];
fgets(size_str,5,stdin);
sscanf(size_str,"%d\n",&size);
Note that it might be safe to stop the program if the value entered is too large. Here we allow from 0 up to 999.
Note also that you have to do the same change some lines below.
instead of:
scanf("%d", &classStudent[i].marks[j]);
write:
char mark_str[5];
fgets(mark_str,5,stdin);
sscanf(mark_str,"%d\n",&classStudent[i].marks[j]);
Hope this helps.