# include <stdio.h>

int mian(void)
{
    int i,j;

    scanf("%d,%d", &i, &j);

    if (i > j)
        printf("i 大于 j\n");
    else
        printf("i 小于 j\n");
    return 0;
}
--------------------Configuration: if...else的用法 - Win32 Debug--------------------
Linking...
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/if...else的用法.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

if...else的用法.exe - 2 error(s), 0 warning(s)

# include <stdio.h>

int main(void)
{
    int i,j;

    scanf("%d,%d", &i, &j);

    if (i > j)
        printf("i 大于 j\n");
    else
        printf("i 小于 j\n");
    return 0;
}

main  不是  mian

主函数都会打错，楼主仔细点吧，别急慢慢打