#include "stdio.h"char* strcat(char s1[],char s2[]){ int i,j; for(i=0;s1[i]!=0;i++) ; for(j=0;s2[j]!=0;i++,j++) s1[i]=s2[j]; s1[i]=0; return s1;}int main(){ char s1[100]="abc",*s; s=strcat(s1,"def"); printf("%s",s); return 0;}