Concatenate two strings using C

#include <stdio.h>
#include <string.h>
 main()
{
   char a[100], b[100];

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

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

   strcat(a,b);

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