#include <stdio.h>
#include <string.h>
int main()

{
char s1[100], s2[100];
int i, j=0;;
printf("\n Please Enter the First String : ");
gets(s1);
printf("\n Please Enter the Second String : ");
gets(s2);

i = strlen(s1);

while( s2[j]!='\0')
{
s1[i] = s2[j];
i++;
j++;
}

s1[i] = '\0';

printf("\n String after the Concatenate = ");
puts(s1);
return 0;
}
     
           
Note: Need to be arranged in compiler after copied
   

 OutPut:

Please Enter the First String : Hello Please Enter the Second String : World String after the Concatenate = Hello World