#include<stdio.h>

int string_concatenate(int i,char a[],char b[])
{
int j=0;


while( b[j]!='\0')
{
a[i] = b[j];
i++;
j++;
}
a[i]='\0';
return a;

}

int string_length(char string[] )
{
int p=0;
while(string[p]!='\0')
{
p++;

}
return p;
}

void main()
{

char s1[100], s2[100];
int l;
printf("\n Please Enter the First String : ");
gets(s1);
printf("\n Please Enter the Second String : ");
gets(s2);

l=string_length(s1);
printf("\nThe concatenated string is: ");
string_concatenate(l,s1,s2);
puts(s1);

}
     
           
Note: Need to be arranged in compiler after copied
   

 OutPut:

Please Enter the First String : Hii Please Enter the Second String : Hello The concatenated string is: HiiHello