I am quite new to programming. Memory allocation also, still confuses me. And our professor asked us to make an array of structures wherein users will input the array size. This is to know how many entries will the users enter in the telephone directory.
Here is it so far:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct TelDirectory {
char name[50];
char address[100];
char tel[20];
};
int main() {
int num, add, del, prev = 0;
char ask;
*//asking for the number of entries*
printf("Number of entries: ");
scanf(" %i", &num);
struct TelDirectory *entry[num];
Input(entry, prev, num);
Display(entry, num);
//Input and Displaying
void Input(struct TelDirectory *entry[], int prev, int num) {
int i;
for (i = prev; i < num; i++) {
entry[i] = (struct TelDirectory *)malloc(sizeof(struct TelDirectory) * num);
printf("\nEnter name (last, first, middle): ");
scanf(" %[^\n]", entry[i]->name);
printf("Enter address: ");
scanf(" %[^\n]", entry[i]->address);
printf("Enter telephone number: ");
scanf(" %[^\n]", entry[i]->tel);
}
void Display(struct TelDirectory *entry[], int num) {
int i, j;
printf("%i\n", num);
struct TelDirectory *temp;
temp = (struct TelDirectory *) malloc(sizeof(struct TelDirectory) * num);
for (i = 0; i < num; i++) {
for (j = i+1; j < num; j++) {
if (strcasecmp(entry[i]->name, entry[j]->name) > 0) {
temp = entry[i];
entry[i] = entry[j];
entry[j] = temp;
}
}
}
printf("\n\t\t\t\t\tInformation\n");
printf("------------------------------------------------------------------------------------------------\n");
printf("Name\t\t\t\t\tAddress\t\t\t\t\tTelephone Number\n");
printf("------------------------------------------------------------------------------------------------\n");
for (i = 0; i < num; i++) {
printf("%-30s\t\t%-30s\t\t%-30s\n", entry[i]->name, entry[i]->address, entry[i]->tel);
}
printf("------------------------------------------------------------------------------------------------\n");
}
And, we will also be asking the users if they will update the directory through either INSERTING more entries or DELETING entries. Is it possible to change the structure array size on run time?
Related
I have to sort this strucure in descending order, based on the "med" variable stored in this strucure, so if students 1 med > students 2 med, then the struct shall be printed as : * student 2 info * then * student 1 info *
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct om
{
char name[20];
int n1,n2,n3;
float med;
} a[3];
int main()
{
int i;
printf("Student's data");
for (i=0; i<3; i++)
{
printf("\nName:");
scanf("%s", a[i].name);
printf("\nGrade at maths:");
scanf("%d", &a[i].n1);
printf("\nGrade at programming:");
scanf("%d", &a[i].n2);
printf("\nGrade at english:");
scanf("%d", &a[i].n3);
a[i].med=(a[i].n1+a[i].n2+a[i].n3)/3;
}
}
Here is an example of how to do this, try to understand how the sorting function works based on some example inputs:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define NUM_STUDENTS 3
struct student
{
char name[20];
int math, prog, engl;
double avg;
} students[NUM_STUDENTS];
static int compare_students(const void *s1, const void *s2)
{
double avg1 = ((struct student *)s1)->avg;
double avg2 = ((struct student *)s2)->avg;
return (avg1 > avg2) - (avg1 < avg2);
}
int main()
{
printf("Student data:\n");
for (int i=0; i<NUM_STUDENTS; i++)
{
printf("Name:");
scanf("%s", students[i].name);
printf("Grade at maths:");
scanf("%d", &students[i].math);
printf("Grade at programming:");
scanf("%d", &students[i].prog);
printf("Grade at english:");
scanf("%d", &students[i].engl);
students[i].avg = (double)students[i].math + students[i].prog + students[i].engl) / NUM_STUDENTS;
}
qsort(students, NUM_STUDENTS, sizeof(struct student), compare_students);
for (int i=0; i<NUM_STUDENTS; i++)
{
printf("Student %d: %s\n", i, students[i].name);
}
return 0;
}
I have also tried to make some general improvements, like adding a #define for the number of students, using more readable variable names and using double instead of float variables (using the latter almost never makes sense in practice). Also note that your average calculation was wrong before because the result was truncated.
man_d_sort(struct om a[])
{
if (a[0].med >= a[1].med)
{
if (a[0].med >= a[2].med)
printf("%.2lf", a[0].med);
else
printf("%.2lf", a[2].med);
}
else
{
if (a[1].med >= a[2].med)
printf("%.2lf ", a[1].med);
else
printf("%.2lf ", a[2].med);
}
}
I must create a program focusing on the use of structures.
The program will ask the user to enter the number of students for whom he will later add specific information (name, surname, average grade).
For some reason, when I start the the program, I enter the number of students i want, after that I enter the info of the first student and then the program terminates.
Here's what I've tried.
#include <stdio.h>
#include <stdlib.h>
struct student
{
char *name;
char *surname;
float *average;
};
void inputs(struct student *a, int size);
int main()
{
int size;
printf("Enter the number of students: ");
scanf("%d", &size);
struct student *data;
data = (struct student *)malloc(size*sizeof(struct student));
if(data==NULL) {
printf("Cannot allocate memory. The program will now terminate.");
return -1;
}
inputs (data, size);
return 0;
}
void inputs(struct student *a, int size)
{
int j=0;
int i;
for(i=0; i<size; i++) {
printf("Enter the name of the student number %d: ", j+1);
scanf("%s", a->name);
printf("Enter the surname of the student number %d: ", j+1);
scanf("%s", a->surname);
printf("Enter the average grade of the student number %d: ", j+1);
scanf("%f", a->average);
j++;
a++;
}
}
This code works:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct student
{
char name[30];
char surname[30];
float average;
};
void inputs(struct student *a, int size);
int main()
{
int size;
int i=0; // we need i
char string[100];
printf("Enter the number of students: ");
// scanf can be tricky lets use fgets
fgets( string , 99 , stdin );
size= atoi(string);
struct student **data; // array of struct
// get memory for the pointers to pointer
data=(struct student **) calloc( size , sizeof(char *));
// now each struct need space
for( i=0 ; i<size ; i++)
{
data[i] = malloc(sizeof(struct student));
if(data[i]==NULL) {
printf("Cannot allocate memory. The program will now terminate.");
return -1;
}// end if
}// end for loop
// input each student
for( i=0 ; i<size ; i++)
inputs (data[i], i );
return 0;
}
void inputs(struct student *a, int num)
{
int j=0;
char string[100];
// scanf can be tricky lets use fgets
printf("Enter the name of the student number %d: ", num+1);
fgets(a->name, 29, stdin);
printf("Enter the surname of the student number %d: ", num+1);
fgets( a->surname , 29, stdin);
printf("Enter the average grade of the student number %d: ", num+1);
fgets( string , 99, stdin);
a->average=atof(string);
}
I have a code like this for a student management system. The input function works fine but I haven't figured out why my output function stop immediately when i call it.( I know that i can not return a local array from a function in C, but i assign the array to a pointer and return that pointer, is it ok?)
Here is my code:
struct Student
{
char name[50];
char birth[25];
char gender[10];
float math, physics;
};
struct Student* input(int n, struct Student *p)
{
int i, id = 1;
struct Student s[n];
getchar();
for(i = 0; i < n; i++)
{
printf("Name: ");
fgets(s[i].name, 50, stdin);
s[i].name[strlen(s[i].name)-1] = '\0';
printf("Date of birth: ");
fgets(s[i].birth,25,stdin);
s[i].birth[strlen(s[i].birth)-1] = '\0';
printf("Gender: ");
fgets(s[i].gender,10,stdin);
s[i].gender[strlen(s[i].gender)-1] = '\0';
printf("Math = ");
scanf("%f", &s[i].math);
printf("Physics = ");
scanf("%f", &s[i].physics);
getchar();
}
p = s;
return p;
}
void outPut(int n, struct Student *p)
{
int i;
for(i = 0; i < n; i++)
{
printf("%s %s %s %f %f\n", p[i].name, p[i].birth, p[i].gender, p[i].math, p[i].physics);
}
}
int main()
{
int n;
struct Student *p, *p1;
int choice;
printf("-----------Student Management-----------");
printf("\n1. Add new students.\n2. Print student list.\n");
do
{
printf("Your choice = ");
scanf("%d", &choice);
switch(choice)
{
case 1:
printf("Number of students = ");
scanf("%d", &n);
input(n,p);
break;
case 2:
outPut(n,p);
break;
}
}
while(choice!=0);
return 0;
}
You are defining your array as a local variable. It means that it will no longer exist after the function ends. To avoid this, declare your array as a pointer and use malloc to initialize it:
struct Student *s = malloc(sizeof(Student) * n);
It will behave as a regular array and you will be able to use itself as the function return.
I'm trying to create a program with a loop that prompts the user to enter data in the array elements. And when the user no longer can enter data, print to screen the data entered in a last in, first out order.
And this is my attempt...
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>
struct Name_Age
{
char Name[10];
int Age;
};
void printMe(struct Name_Age info)
{
printf("Name: %s\n", info.Name);
printf("Age: %d\n", info.Age);
}
int main()
{
int size = 0, i = 0, j = 0;
struct Name_Age * array_ptr = (struct Name_Age*)malloc((size + 1)* sizeof(struct Name_Age));
struct Name_Age myInfo = *array_ptr;
printf("Enter size of array: ");
scanf("%d\n", size);
for (i = 0; i < size; ++i)
{
printf("Enter Name: \n");
scanf("%s\n", myInfo.Name);
printf("Enter Age: \n");
scanf("%d\n", myInfo.Age);
}
printMe(myInfo);
return 0;
};
First, scanf("%d", &size) replace scanf("%d\n", size), put &size instead of size as argument(You need an address), and put the malloc things after this line of code, because you need an exact size value before malloc. Same thing with all the scanf stuffs.
As you want to print out all your input names and ages in order, I changed your code like this:
#include <stdio.h>
#include <stdlib.h>
struct Name_Age
{
char Name[10];
int Age;
};
void printMe(struct Name_Age *infoList, int size)
{
int i;
for (i = size-1; i >= 0; --i)
{
printf("Name: %s\n", infoList[i].Name);
printf("Age: %d\n", infoList[i].Age);
printf("\n");
}
}
int main()
{
int size, i;
printf("Enter size of array: ");
scanf("%d", &size);
struct Name_Age * array_ptr = (struct Name_Age*)malloc(size* sizeof(struct Name_Age));
for (i = 0; i < size; ++i)
{
printf("Enter Name: \n");
scanf("%s", array_ptr[i].Name);
printf("Enter Age: \n");
scanf("%d", &array_ptr[i].Age);
}
printMe(array_ptr, size);
return 0;
}
Try to test and compare with your code, questions are welcome.
You can use fgets to read strings and cast the string to digits with atoi. The storage is not complete, but with my changes you can read to structs and specify the size of the loop (TODO: Save a list of structs so that you actually can print a list of structs that you have specified.)
#include <stdio.h>
#include <stdlib.h>
struct Name_Age {
char Name[10];
int Age;
};
void printMe(struct Name_Age info) {
printf("Name: %s\n", info.Name);
printf("Age: %d\n", info.Age);
}
int main() {
int size = 0, i = 0, j = 0;
struct Name_Age *array_ptr = malloc((size + 1) * sizeof(struct Name_Age));
struct Name_Age myInfo = *array_ptr;
printf("Enter size of array: ");
char tmp[10];
fgets(tmp, 10,stdin);
size = atoi(tmp);
for (i = 0; i < size; ++i) {
printf("Enter Name: ");
fgets(myInfo.Name, 10,stdin);
printf("Enter Age: ");
fgets(tmp, 10,stdin);
myInfo.Age = atoi(tmp);
}
printMe(myInfo);
return 0;
};
Test
$ ./a.out
Enter size of array: 2
Enter Name: Superman
Enter Age: 25
Enter Name: Batman
Enter Age: 27
Name: Batman
Age: 27
See also this question about fgets fgets how to read int
Obviously using fgets() is a much better approach, but making the fewest amount of changes as possible to your code and still achieving your result is the following:
#include <stdio.h>
#include <stdlib.h>
struct Name_Age
{
char Name[10];
int Age;
};
void printMe(struct Name_Age *info);
int main(void)
{
int size, i;
struct Name_Age *array_ptr;
printf("Enter size of array: ");
scanf("%d", &size);
array_ptr = malloc(size * sizeof *array_ptr);
for (i = 0; i < size; ++i)
{
printf("Enter Name: ");
scanf(" %s", array_ptr[i].Name);
printf("Enter Age: ");
scanf("%d", &array_ptr[i].Age);
printf("\n");
}
for (i = 0; i < size; ++i)
printMe(&array_ptr[i]);
return 0;
}
void printMe(struct Name_Age *info)
{
printf("Name: %s\n", info->Name);
printf("Age: %d\n", info->Age);
}
Note that passing the struct by pointer to the function should be faster, note that you don't need the myInfo struct; you can just directly modify the elements of the array. Note the space before %s in the scanf() line, this is to discard any whitespace (including \n), this is done automatically for %d so it is only necessary for your strings (technically not the first iteration of the loop, but it doesn't fail if no whitespace is found). If you have any questions about why I made the changes I did, please feel free to comment on this answer!
example of fix
//struct Name_Age myInfo = *array_ptr;//Not necessary
printf("Enter size of array: ");
scanf("%d", &size);//remove `\n`, add `&`
//To ensure after the size has been determined
struct Name_Age * array_ptr = (struct Name_Age*)malloc(size * sizeof(struct Name_Age));//Cast is not necessary in C
for (i = 0; i < size; ++i)
{
printf("Enter Name: \n");
scanf("%s", array_ptr[i].Name);//remove `\n`
printf("Enter Age: \n");
scanf("%d", &array_ptr[i].Age);//need `&`
}
for (i = 0; i < size; ++i)
printMe(array_ptr[i]);
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.