Question

I have the following program

#include <stdio.h>

main()
{

    char ch[10];

    gets(ch);

    printf("\nTyped: %s\n\n", ch);

    int i = 0;
    while ( ch[i] != '\0' )
    {
        printf("Letter: %c\n", ch[i]);
        i++;
    }

    printf("\nTyped: %s\n\n", ch);


}

and here is the output when i typed “Hello world is good”

hello world is good

Typed: hello world is good

Letter: h
Letter: e
Letter: l
Letter: l
Letter: o
Letter:
Letter: w
Letter: o
Letter: r
Letter: l
Letter:


Typed: hello worl♂

Why i am getting two different output for same command after while loop? does while loop has anything to do with it.. please help..

Answer 1

Your character array ch only has space for 10 chars. You typed something longer than 10 chars and tried to store it in that array, effectively writing beyond the end of the array into space that’s not reserved for anything (or at least isn’t reserved for your characters). You got lucky in this case and didn’t write over anything important (your program didn’t crash), but subsequent code comes along (the printf(), your int i, etc.) and changes that memory (it’s the stack, after all, so it gets used in FIFO order).

Change your char ch[10] to char ch[2048] to give yourself a larger buffer to type into. You might also use fgets() instead of gets() so that you can limit the size of the input to your buffer size. If you use gets(), heed the warning on the man page:

It is the caller’s responsibility to ensure that the input line, if
any, is sufficiently short to fit in the string.