Question

I know that every string in C ends with ‘\0’ character. It is very useful in cases when we need to know when the string ends. However, I am unable to comprehend its use in printing a string and printing a string without it. I have the following code:-

/* Printing out an array of characters */
#include<stdio.h>
#include<conio.h>
int main()
{
    char a[7]={'h','e','l','l','o','!','\0'};
    int i;
    /* Loop where we do not care about the '\0' */ 
    for(i=0;i<7;i++)
    {
        printf("%c",a[i]);
    }
    printf("\n");
    /* Part which prints the entire character array as string */
    printf("%s",a);
    printf("\n");
    /* Loop where we care about the '\0' */
    for(i=0;i<7&&a[i]!='\0';i++)
    {
        printf("%c",a[i]);
    }
}

The output is:-

hello!
hello!
hello!

I am unable to understand the difference. any explanations?

Answer 1

In this case:

for(i=0;i<7;i++)
{
    printf("%c",a[i]);
}

You loop for a number of times (7) and then quit. That is the end condition of the loop. It terminates, no matter anything else.

In the other case, you also loop for 7 times and no more and you just added another condition, which really serves no function as you already keeping a count of things. If you did the following:

 int index = 0;
 while (a[index] != '\0') { printf("%c", a[index]); index++; } 

now you would depend on the zero termination character being there, if it wasn’t in the string, you while loop would go on forever until the program crashed or something terminated it forcedly. Probably printing garbage on your screen.