Question

When I run this on my computer I get compile errors. However, I did copy it straight from a tutorial I found on the Internet.

#include <stdio.h>
#include <conio.h>

void main(){
    int i = 9;
    clrscr();

    printf("The value of i is: %d\n", i);
    printf("The address of i is: %u\n", &i);
    printf("The value at the address of i is: %d\n", *(&i));

    getch();
}

The errors:

$ cc "-Wall" -g    ptrex6.c   -o ptrex6
ptrex6.c:7:19: error: conio.h: No such file or directory
ptrex6.c:9: warning: return type of ‘main’ is not ‘int’
ptrex6.c: In function ‘main’:
ptrex6.c:11: warning: implicit declaration of function ‘clrscr’
ptrex6.c:14: warning: format ‘%u’ expects type ‘unsigned int’, but argument 2 has type ‘int *’
ptrex6.c:17: warning: implicit declaration of function ‘getch’
make: *** [ptrex6] Error 1

Answer 1

Mistakes:

1. conio.h is not a standard C header. It might be unavailable on your system. Nevertheless, it’s not needed for printf(). That’s why stdio.h is here. Remove it, and also remove clrscr(). It won’t work without the conio libraries. By doing this, you’ll able to compile your file, since the other messages are “just” warnings, not errors.

2. Change your main() function’s return type to int and return 0. That’s what the C standard specifies. You want this.

3. Use the %d format specifier in place of %u. As the compiler message directly points out, %u is for unsigned integers, and int is explicitly signed. For integers >= 2 ^ 31, you’ll experience strange behavior problems.

4. You’re using a wrong specifier one more time. Use %p for addresses/pointers, not %u/%d/whatever.

5. Don’t explicitly believe/copy-paste from tutorials. Tutorials are not for copy-pasting, they’re to be thought of and learnt from.