程序代码：

#include <stdio.h>

void strcat_link( char s1[], const char s2[] );

int main( void )
{
    char str1[20] = "beijing";
    char str2[20] = "shanghai";
    strcat_link( str1, str2 );
    printf( "str1:%s\nstr2:%s\n", str1, str2 );

    return 0;
}

void strcat_link( char s1[], const char s2[] )
{
    for( ; *s1; ++s1 );
    for( ; *s1++=*s2++; );
}