C Tutorial/string.h/strcat
strcat
Item Value Header file string.h Declaration char *strcat(char *str1, const char *str2); Function concatenates a copy of *str2 to *str1 and terminates *str1 with a null. Return returns *str1.
You have to ensure that str1 is large enough to hold both its original contents and those of str2.
#include <stdio.h>
#include <string.h>
int main(void)
{
char s1[80], s2[80];
printf("s1:");
gets(s1);
printf("s2:");
gets(s2);
strcat(s2, s1);
printf(s2);
return 0;
}