I'm a C beginner and am working on a program that registers flights using structs. Each flight has a code that must follow a certain structure: FLI-XXXX, X being integers. I'd like to use the integers part of the code later on, so I thought the best way to scan for it was using both fgets and scanf. After validating the code using auxiliary variables, I would later write it to the flights struct. However, I'm stuck at the validating part.
The problem is, whenever I call the function that validates a code (opt1) inside an if statement, it runs twice and only works as intended the second time around. Here's my code:
#include <stdio.h>
#include <string.h>
typedef struct
{
int num;
char code[5];
}fl;
fl flight[9999];
int Valid(char a[], int b)
{
if((strlen(a) != 4) || (b<0 || b>9999)){
return 0;
}
else if(a[0] !='F' || a[1] !='L' || a[2] !='I' || a[3] != '-'){
return 0;
}
return 1;
}
void opt1(fl a[]){
char tempCode[5];
int tempNum;
do
{
puts("Insert code:");
fgets(tempCode, 5, stdin);
scanf("%d", &tempNum);
puts("");
if (Valid(tempCode, tempNum))
{
printf("Flight %s%d registered. \n", tempCode, tempNum);
}
else
{
puts("Flight # invalid.");
}
} while (Valid(tempCode, tempNum)==0);
}
int main() {
int opt;
//calling opt1 works as intended
opt1(flight);
//calling inside if statement runs opt1() twice, only the second time as intended
scanf("%d", &opt);
if(opt==1){
opt1(flight);
}
return 0;
}
And here's an input:
FLI-1234
1
FLI-1234
That returns:
Flight FLI-1234 registered.
Insert code:
Flight # invalid.
Insert code:
Flight FLI-1234 registered.
I'm not sure why this is happening. Can anyone guide me in the right direction, please? Thank you.
Related
I'm working on the last exercise of the "Think like a computer scientist, C version" book and I have some trouble with one particular point.
The exercise consists of making a small game, where the computer picks a random value between 0 and 20 and then asks me to guess the number.
After that, the computer counts the number of tries I made and, if I get a better score than the previous party, I need to store my name and the number of tries in a structure.
My problem is the following: When I restart the game, the string value, player_name, in the structure gets somehow deleted but player_score is still there.
First, I made a "call by value" function to create the structure and then a tried with a "call by reference" but getting the same results.
I think I tried everything I could with my actual knowledge for now; so, if someone could check my code and give me some tips about what's wrong I would much appreciate it!
//HEADERS
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define FALSE 0
#define TRUE 1
//TYPEDEF STRUCTS
typedef struct
{
int player_score;
char *player_name;
} HS_Player;
//FUNCTION PROTOTYPES
int Random_Value(void);
int Get_User_Choice(void);
int Check_Result(int computer, int my_choice);
int Try_Again(int game_result, int computer);
void Player_Infos(HS_Player *player_p, int score);
int Game_Restart(void);
//MAIN
int main(void)
{
int end_game;
int high_score_value = 100;
HS_Player player;
while (end_game != TRUE)
{
int computer_number = Random_Value();
printf("Guess the number between 0 et 20 chosen by the computer.\n");
int your_number = Get_User_Choice();
int result_game = Check_Result(computer_number, your_number);
int tries_to_win = Try_Again(result_game, computer_number);
printf("Number of tries: %i\n", tries_to_win);
if (tries_to_win < high_score_value)
{
Player_Infos(&player, tries_to_win );
high_score_value = player.player_score;
}
printf("Highest score: %i By: %s\n", player.player_score, player.player_name);
printf("\n");
end_game = Game_Restart();
}
return EXIT_SUCCESS;
}
//Random_Value FUNCTION
int Random_Value(void)
{
srand(time(NULL));
int x = rand();
int y = x % 20;
return y;
}
//Get_User_Choice FUNCTION
int Get_User_Choice(void)
{
int success, x;
char ch;
printf("Your Guess:\t");
success = scanf("%i", &x);
while (success != 1)
{
printf("Your input is not a number. Please try again:\t");
while ((ch = getchar()) != '\n' && ch != EOF);
success = scanf("%i", &x);
}
if (x < 0 || x > 20)
{
printf("Your input must be between 0 and 20. Please try again.\n");
Get_User_Choice();
}
return x;
}
//Check_Result FUNCTION
int Check_Result(int computer, int my_choice)
{
int check_result;
if (my_choice < computer)
{
printf("Computer number is larger!\n");
check_result = FALSE;
}
else if (my_choice > computer)
{
printf("Computer number is smaller!\n");
check_result = FALSE;
}
else if (my_choice == computer)
{
printf("It's a Match! You chose the same number than the computer.\n");
printf("\n");
check_result = TRUE;
}
return check_result;
}
//Try_Again FUNCTION
int Try_Again(int game_result, int computer)
{
int tries_befor_success = 1;
while (game_result != TRUE)
{
int your_number = Get_User_Choice();
game_result = Check_Result(computer, your_number);
tries_befor_success++;
}
return tries_befor_success;
}
//Player_Infos FUNCTION
void Player_Infos(HS_Player *player_p, int score)
{
char new_name[80];
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
scanf("%s", new_name);
printf("\n");
player_p->player_score = score;
player_p->player_name = new_name;
}
//Game_Restart FUNCTION
int Game_Restart(void)
{
int quit_value;
printf("Quit Game ?\n");
printf("Press 'y' to quit or any other keys to continue.\n");
fflush(stdin);
char quit_game = getchar();
printf("\n");
if (quit_game == 'y')
{
quit_value = TRUE;
}
else
{
quit_value = FALSE;
}
return quit_value;
}
The problem is that, in your Player_Infos function, you are assigning the address of a local array to the char* player_name pointer member of the passed structure. When that function ends, the local array it used will be deleted and the pointer in the structure will be invalid. (In the case of the player_score, you don't have that problem, because the given value is copied to the structure member.)
There are several ways around this; one would be to use the strdup() function to make a copy of the local char new_name[80]; array – but that is really overkill, and you would need to manage (i.e. free()) that allocated string whenever you make a modification.
A simpler way is to make the player_name member an actual array of char and then use strcpy() to copy the local array into that member.
Better, still, with the player_name member defined as char [80], you can read directly into that (in the function), and avoid the local array completely:
typedef struct
{
int player_score;
char player_name[80];
} HS_Player;
//...
void Player_Infos(HS_Player *player_p, int score)
{
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
// Read directly. Limit input to 79 chars (allowing room for null terminator).
scanf("%79s", player_p->player_name);
printf("\n");
player_p->player_score = score;
}
Also, just as a "style" tip, you may want to change the member names to just score and name, as the "player" part is implied by the structure type-name itself.
This issue you are having is that you are associating the player name pointer to a variable that goes out of scope when you leave the "player_Infos" function. What you probably would want to do is define the name as a character array in your structure and then use the "strcpy" call in your function instead. Following is a couple of code snippets illustrating that point.
//TYPEDEF STRUCTS
typedef struct
{
int player_score;
char player_name[80];
} HS_Player;
Then, in your function, use the "strcpy" call.
//Player_Infos FUNCTION
void Player_Infos(HS_Player *player_p, int score)
{
char new_name[80];
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
scanf("%s", new_name);
printf("\n");
player_p->player_score = score;
strcpy(player_p->player_name, new_name);
//player_p->player_name = new_name;
}
When I tested that out, I got a name to appear in the terminal output.
Computer number is smaller!
Your Guess: 4
It's a Match! You chose the same number than the computer.
Number of tries: 8
Highest score: 4 By: Craig
FYI, you will need to include the "string.h" file.
Give that a try.
Name Update
The reason your player.player_name is not getting updated is because you can't assign a string this way in C. When doing player_p->player_name = new_name; you're actually saving in player_p->player_name the memory address of new_name.
Instead, what you want to achieve, is to copy each character of new_name to player_p->player_name and in order to achieve this, you have to change the type of prlayer_name field from char* player_name to char player_name[80], then assign it using, for example, strcpy():
#include <string.h>
// [...]
//TYPEDEF STRUCTS
typedef struct
{
unsigned int player_score;
char player_name[80];
} HS_Player;
// [...]
//Player_Infos FUNCTION
void Player_Infos(HS_Player *player_p, int score)
{
char new_name[80];
printf("Congrats! Your made a new high score.\n");
printf("What's your name ?\t");
scanf("%s", new_name);
printf("\n");
player_p->player_score = score;
strcpy(player_p->player_name, new_name);
}
Data Persistence
To make data (players info) persistent over multiple runs, you have to save the content of the struct to a file.
Example
int Save_Score(char* filename, HS_Player* player)
{
FILE* file = fopen(filename, "w");
if (file == NULL)
{
fprintf(stderr, "\nAn error occurred while opening the file\n");
return -1;
}
if (fprintf(file, "%d %s", player->player_score, player->player_name) < 0)
return -1;
fclose(file);
return 0;
}
int Load_Score(char* filename, HS_Player* player)
{
FILE* file = fopen(filename, "r");
if (file == NULL)
{
fprintf(stderr, "\nAn error occurred while opening the file\n");
return -1;
}
if (fscanf(file, "%d %79s", &player->player_score, player->player_name) < 0)
return -1;
fclose(file);
return 0;
}
What am I doing wrong? My code keeps in loop and n goes minus. It was supposed to return 0; at 0.Also whatever I do it starts with 3-2-1-0 even I type "2" it still keeps doing it 3-2-1-0
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
static const char PSWRD[]="1234";
char p[6];
int n=3, y;
printf("Hos geldiniz");
do{
printf("\n\nOgrenci_ID:Elif");
fflush(stdout);
printf("\nSifre:");
scanf("%s", &p);
fflush(stdout);
y=strcmp(p, PSWRD);
if(y==0){
printf("\nGiris Basarili"); `//succesfull login`
return 0;
}else {
printf("Yanlis Sifre, tekrar deneyiniz", 3-n); //wrong password try again
printf("\nKalan hakkiniz ");
printf("%d\n", n);
getchar();
n--;}
if(n<1){
printf("\nHesabiniz bloke oldu");
return 0;
// that means you use all your chance and now you're blocked but my code aint stop here and n goes minus
}
// I am not exactly sure about "3"
//Also what ever i do it starts with 3-2-1-0 even i type "2" it's still keep doing it 3-2-1-0
}while (n<=3);
return 0;
}
while (n<=3);
doesn't agree with
n--;
You seem to want
while (n>0);
Its working for me!
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
int main()
{
static const char PSWRD[]="1234";
char p[6];
int n=3, y;
printf("Welcome");
do{
printf("\n\nStudent_ID:Elif");
fflush(stdout);
printf("\nPassword:");
scanf("%s", p);
fflush(stdout);
y=strcmp(p, PSWRD);
if(y==0){
printf("\nSucessfull Login\n"); //succesfull login
return 0;
}else{
n--;
printf("\nWrong password, try again: "); //wrong password try again
printf("\nRemaining attempts ");
printf("%d\n", n);
getchar();
}
if(n<1){
printf("\nYour account has been blocked\n");
return 0;
}
}while (n>0);
}
When user introduces wrong password, you have more 2 tries and if you enter the password wrong on thats 2 tries program ends! But if you insert it right program makes login, so works fine
In your code, there is no increment of 'n', so the loop keeps going (because n is always smaller than 3). I'm not too sure of what you're trying to do, but you need to change your 'while' condition or statements of 'n' inside the loop.
Currently the loop keeps running forever:
When n=3 - > 3<=3 is true.
When n=2 - > 2<=3 is true.
Etc.
The only way it's going to end is when n decrements until it is equal to the absolute minimum value of an integer which is -2,147,483,648, then it will decrement one more time and change to 2,147,483,647 and the loop will end.
Use printf to watch the value of n, and you will quickly observe that your condition for the do...while loop is incorrect.
However, note the conditional, if(n<=0) with return.
Provide a minimal reproducible example, such as below...
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int login(char* PSWRD)
{
int n=3, y;
char p[100+20];
printf("Hos geldiniz");
do{
printf("\nSifre:");
scanf("%100s", p); // limit input size, use p, not &p
if( 0 == strcmp(p, PSWRD) ) {
printf("\nsuccess!");
return 0;
}
printf("Yanlis Sifre, tekrar deneyiniz"); //wrong password try again
n--;
if(n<=0)
{
printf("\nHesabiniz bloke oldu");
return -1;
}
printf("n=%d\n",n); // print current n
} while (n<=3); // this should be (n>0)
return -1;
}
int main()
{
char* PASSWD = "password";
int result;
if( 0 > login(PASSWD) ) {
printf("\nfailed!\n");
exit(1);
}
printf("\nsuccess!\n");
// continue processing here
}
Caveat: Make sure you limit input size to avoid buffer overflow
Read no more than size of string with scanf()
I am currently trying to store information that is input from a function to a struct declared in my header file and utilize it within the main file. I cannot use struct arrays because I am not allowed to allocate memory.
header file
#ifndef HOMEWORK_H_
#define HOMEWORK_H_
typedef struct
{
int CourseID[25];
char CourseName[100][25];
}Course;
void NewCourse(void);
#endif
My code
#include <stdio.h>
#include <stdlib.h>
#include "Homework.h"
void NewCourse()
{
int i;
int CNumber = 0;
Course storeC;
for(i = 0; i < 0; i++)
{
if(storeC.CourseID[i] == 0)
{
if(storeC.CourseName[i] == NULL)
{
int CNumber = i;
break;
}
}
}
printf("%d\n", CNumber);
printf("Please enter the course's ID number: ");
scanf("%d", &storeC.CourseID[CNumber]);
printf("Please enter the course's name: ");
scanf("%s", storeC.CourseName[CNumber]);
}
and my main does not really apply since the problem lies within storing the data.
A few things to keep in mind is I must utilize a separate file for my functions and I must use a header file for my structs.
I know my for loop to determine where in the array may not be effective, but I am not so worried about it as of right now.
My question is how do I store the data from this function to the
header file?
Update
I changed the main function to fit everything else and I end up with this error now.
a label can only be part of a statement and a declaration is not a
statement
The code in main is:
switch(Option)
{
case 1:
Course c = NewCourse();
printf("%d\n%s\n", c.CourseID[0], c.CourseName[0]); // For testing purposes
break;
What is causing the error because it says it stems from line 29 which is the Course c = NewCourse();?
Change NewCourse to return a Course.
Course NewCourse(void);
Change the implementation to:
Course NewCourse()
{
int i;
int CNumber = 0;
Course storeC;
...
return storeC;
}
Change main accordingly.
int main()
{
Course c = NewCourse();
}
PS
You said,
I cannot use struct arrays because I am not allowed to allocate memory.
I assume that to mean that you cannot use dynamic memory allocation. If you are allowed to create an array of structs in the stack, you can simplify your code by using:
typedef struct
{
int CourseID[25];
char CourseName[100];
}Course;
void NewCourse(Course course[]);
and in main, use:
Course courses[25];
NewCourse(courses)
In response to your update
You needed to add a scope block { } around the code as follows:
int main()
{
{
Course c = NewCourse();
}
}
This should resolve your error and allow your code to compile.
Additionally, you have an error in manipulating the CNumber Variable. It is declared twice, with different scopes:
int CNumber = 0; // the first definition with the scope of the NewCourse Function
Then inside the test, with a block scope:
if(storeC.CourseID[i] == 0)
{
if(storeC.CourseName[i] == NULL)
{
int CNumber = i; // block-scope. This is not the same CNumber Variable (todo: Omit int)
break;
}
}
As a result, when you reference it later in
printf("%d\n", CNumber);
printf("Please enter the course's ID number: ");
scanf("%d", &storeC.CourseID[CNumber]);
printf("Please enter the course's name: ");
scanf("%s", storeC.CourseName[CNumber]);
It will be always reference the function scope variable, which is always be zero.
Solution: omit the int declaration inside the test:
if(storeC.CourseName[i] == NULL)
{
CNumber = i;
break;
}
I am having a lot of trouble wrapping my head around calling functions and using them in the main program again later. I have not found an answer in depth to explain why this doesn't run. I understand that parameters belong inside of the called function parentheses, but I want the user input to begin in the called program. Is this even possible? Theoretically, the function would ask the user for a year, check that it is within certain parameters, then return it to the main function where I would like to eventually be able to store it in an array. For now, can someone please show me how I would make that work in this elementary program? Thank you in advance!
#include <stdio.h>
char year_info();
int main(void)
{
int menu_selection;
char year;
printf("Please choose from the following menu: \n1. Insert a new movie\n2. Show movie\n3. List all\n4. Exit\n");
scanf("%i", &menu_selection);
switch (menu_selection)
{
case 1: year = year_info();
printf("%c", year);
break;
}
}
char year_info()
{
int year_input;
printf("\nYear: ");
scanf("%i", &year_input);
if (year_input > 2016 || year_input < 1920)
{
printf("Sorry, I do not recognize this command. Please try again.\n");
}
else
{
int year = year_input;
return year;
}
}
It doesn't run because you're passing scanf the variable, but you should pass the address of the variable, i.e. use:
scanf("%i", &something);
instead of scanf("%i", something);
Also, as others pointed out, you're mixing char and int too liberally, so it won't work as expected.
year and year_imput can't be chars because they won't hold values large enough, you'll need at least a short.
You had 2 errors.
scanf("%i", &menu_selection);
scanf("%i", &year_imput);
You need to use the & to pass the address of the variables to scanf().
Edit: However, I would have used an integer for that, because a scanf("%c", &something) will only recognize the first char you enter, and not the whole string, even if that happened you can't do if (year_imput > 2016 || year_imput < 1920) between strings, you can do that with chars, but again, they can only store one character, so I would have done your program like this.
#include <stdio.h>
int year_info();
int main() {
int menu_selection;
int year;
printf("Please choose from the following menu: \n1. Insert a new movie\n2. Show movie\n3. List all\n4. Exit\n");
scanf("%i", &menu_selection);
switch (menu_selection) {
case 1:
year = year_info();
printf("%i", year);
break;
default:
break;
}
return 0;
}
int year_info() {
int year_imput;
printf("\nYear: ");
scanf("%i", &year_imput);
if (year_imput > 2016 || year_imput < 1920) {
printf("Sorry, I do not recognize this command. Please try again.\n");
return 0;
}
else
return year_imput;
}
I am new to C and very much interested in knowing how to approach any problem which has more than 3 or 4 functions, I always look at the output required and manipulate my code calling functions inside other functions and getting the required output.
Below is my logic for finding a students record through his Id first & then Username.
This code according to my professor has an excessive logic and is lacking in many ways, if someone could assist me in how should I approach any problem in C or in any other language it would be of great help for me as a beginner and yes I do write pseudo code first.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct{
int id; //Assuming student id to be unique
int age;
char *userName; //Assuming student userName to be unique
char *dept;
}student; // Alias "student" created for struct
student* createstruct(); // All function prototype declared
student* createArray();
void addstruct(student* s2);
void searchChar(student* s2,int num);
void searchInt(student* s2,int num);
student* createstruct() // function createStruct() to malloc data of struct student.
{
student *s;
s = (student*)malloc(sizeof(student));
s->userName = (char*)malloc(sizeof(char)*32);
s->dept = (char*)malloc(sizeof(char)*32);
printf("please enter id ");
scanf("%d",&s->id);
printf("please enter age ");
scanf("%d",&s->age);
printf("please enter userName ");
scanf("%31s",s->userName);
printf("please enter department ");
scanf("%31s",s->dept);
printf("\n");
return s;
}
student* createArray()
{
student *arr; //declaration of arr poiter, type struct student
arr = (student*)malloc(sizeof(student)*10); // memory allocated for a size of 10
return arr;
}
void addstruct(student *s2) // function for adding data to the structures in array
{
int i,num;
student* s1;
printf("please enter the number of records to add:");
scanf("%d",&num);
printf("\n");
if(num>0 && num<11)
{
for(i=0;i<num;i++) // if user want to enter 5 records loop will only run 5 times
{
s1 = createstruct();
s2[i].id = s1->id; // traversing each element of array and filling in struct data
s2[i].age = s1->age;
s2[i].userName = s1->userName;
s2[i].dept= s1->dept;
}
}
else if(num>10) // if user enters more than 10
{
for(i=0;i<10;i++) // loop will still run only 10 times
{
s1 = createstruct();
s2[i].id = s1->id;
s2[i].age = s1->age;
s2[i].userName = s1->userName;
s2[i].dept = s1->dept;
}
printf("Array is full"); // Array is full after taking 10 records
printf("\n");
}
searchInt(s2,num); // Calling searchInt() function to search for an integer in records
searchChar(s2,num); // Calling searchChar() function to search for a string in records
free(s1);
free(s2);
}
void searchChar(student* s2,int num) // function for searching a string in records of structure
{
char *c;
int i;
c = (char*)malloc(sizeof(char)*32);
printf("please enter userName to search ");
scanf("%31s",c);
printf("\n");
for (i=0;i<num;i++) //num is the number of struct records entered by user
{
if ((strcmp(s2[i].userName,c)==0)) //using strcmp for comparing strings
{
printf("struct variables are %d, %d, %s, %s\n", s2[i].id,s2[i].age,s2[i].userName,s2[i].dept);
break;
}
else if(i == num-1)
{
printf("nothing in userName matches: <%s>\n",c);
break;
}
}
}
void searchInt(student* s2,int num) //searchs for an integer and prints the entire structure
{
int i,z;
printf("please enter id to search ");
scanf("%d",&z);
printf("\n");
for (i=0;i<num;i++)
{
if (s2[i].id == z)
{
printf("struct variables are %d, %d, %s, %s\n\n", s2[i].id,s2[i].age,s2[i].userName,s2[i].dept);
break;
}
else if(i == num-1)
{
printf("nothing in id matches: <%d>\n\n",z);
break;
}
}
}
int main(void)
{
student *s2;
s2 = createArray();
addstruct(s2);
return 0;
}
I'm not going to go into optimizing, because if you wanted better theoretical performance you would probably go with different data structures, such as ordered arrays/lists, trees, hash tables or some kind of indexing... None of that is relevant in this case, because you have a simple program dealing with a small amount of data.
But I am going to tell you about the "excessive logic" your professor mentioned, taking your searchInt function as an example:
for (i=0;i<num;i++)
{
if (s2[i].id == z)
{
printf("struct variables are %d, %d, %s, %s\n\n", s2[i].id,s2[i].age,s2[i].userName,s2[i].dept);
break;
}
else if(i == num-1)
{
printf("nothing in id matches: <%d>\n\n",z);
break;
}
}
The thing here is that every time around the loop you're testing to see if you're at the last element in the loop. But the loop already does that. So you're doing it twice, and to make it worse, you're doing a subtraction (which may or may not be optimized into a register by the compiler).
What you would normally do is something like this:
int i;
student *s = NULL;
for( i = 0; i < num; i++ )
{
if( s2[i].id == z ) {
s = &s2[i];
break;
}
}
if( s != NULL ) {
printf( "struct variables are %d, %d, %s, %s\n\n",
s->id, s->age, s->userName, s->dept );
} else {
printf("nothing in id matches: <%d>\n\n",z);
}
See that you only need to have some way of knowing that the loop found something. You wait for the loop to finish before you test whether it found something.
In this case I used a pointer to indicate success, because I could then use the pointer to access the relevant record without having to index back into the array and clutter the code. You won't always use pointers.
Sometimes you set a flag, sometimes you store the array index, sometimes you just return from the function (and if the loop falls through you know it didn't find anything).
Programming is about making sensible choices for the problem you are solving. Only optimize when you need to, don't over-complicate a problem, and always try to write code that is easy to read/understand.