Question

Following is my code, I am trying to run it in Visual Studio.

#include <stdio.h>
#include <conio.h>
int main()
{
    //int i;
    //char j = 'g',k= 'c';
    struct book 
    {
        char name[10];
        char author[10];
        int callno;
    };
    struct book b1 = {"Basic", "there", 550};
    display ("Basic", "Basic", 550);
    printf("Press any key to coninute..");
    getch();
    return 0;
}

void display(char *s, char *t, int n)
{
    printf("%s %s %d \n", s, t, n);
}

It gives an error of redefinition on the line where opening brace of function is typed.

Answer 1

You call display before declaring it, and in such cases the compiler assumes the return type is int, but your return type is void.

Declare the function before using it:

void display(char *s, char *t, int n);
int main() {
    // ...

Also note, that you declare it as receiving char*, but pass string literals to it (const char*) either change the declaration, or change the arguments, e.g:

void display(const char *s, const char *t, int n);
int main()
{
    // snip
    display ("Basic", "Basic", 550);
    //snap
}

void display(const char *s, const char *t, int n)
{
    printf("%s %s %d \n", s, t, n);
}