While循环+ fgets错误

Question

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <cstdlib>
int main ()
{
    char ans[100];
    int count;
    count=0;
    char *arr[100];
    char *srtarr[100];

    while(count<100)
    {
        if(strcmp(ans,"done\n")!=0)  
        {      
            printf("Enter names when done type done:");
            fgets(ans,100,stdin);       
            arr[count]=strdup(ans);
        }
        printf("%s",arr[count]);
        count++;
     }

    system("pause");
    return 0;   
}

When I run this code the program stops working. Im very new to c and might have made a few errors. I think the problem is either the while loop or the fgets() function.

EDIT: I corrected the while loop however I'm not understanding how to initialize the array. Doesn't each element within the array get filled as the loop progresses?

Answer 1

You initialize 'count' to 0, hit the while loop and use 'count - 1' as an array index. An array index of -1 definitely could crash your program.

Answer 2

You have at least two cases of undefined behavior in your code:

1. You don't in initialize any of the arrays, meaning the pointers in them are indeterminate.
2. You use a negative index in the first iteration.

Also, you should not forget that fgets leave the newline in the string, so your string comparison will never succeed.

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My recommended solution: A loop while count is less than 100 , then inside the loop check for "done" (or rather "done\\n" ) using ans (before duplicating it) and break out of the loop then.