#include

voidstrcpy(char*s1,char*s2)

{

if(s1==null||s2==null)return;

while(*s2!="\0")*s1++=*s2++;

*s1="\0";

}

voidstrcat(char*s1,char*s2)

{

if(s1==null||s2==null)return;

while(*s1!="\0")s1++;

while(*s2!="\0")*s1++=*s2++;

*s1="\0";

}

intmain(void)

{

chars1[100]="abcd";

chars2[100]="1234";

chars3[100]="uvwxyz";

strcat(s1,s2);

strcpy(s2,s3);

printf("%s\n",s1);

printf("%s\n",s2);

return0;

}