#include<stdio.h> 

int string_concatenate(char *a,char *b)
{

while(*a!='\0')
{
a++;
}

while( *b!='\0')
{
*a = *b;
a++;
b++;
}
*a='\0';

}


void main()
{ char s1[100], s2[100]; int l;
printf("\nEnter the First String : ");
gets(s1);
printf("\nEnter the Second String : ");
gets(s2);

printf("\nThe concatenated string is: ");
string_concatenate(s1,s2);
puts(s1);
}
     
           
Note: Need to be arranged in compiler after copied
   

 OutPut:

Enter the First String : No Enter the Second String : Thing The concatenated string is: NoThing