#include <stdio.h>
#include <string.h>
int main()
{
  char a[1000], b[1000];

  printf("Enter the first string\n");
  gets(a);

  printf("Enter the second string\n");
  gets(b);

  strcat(a, b);

  printf("String obtained on concatenation: %s\n", a);

  return 0;
}

output:

Enter the first string

programming

Enter the second string

skills

String obtained on concatenation:programmingskills