C Program For Operations on Strings (User defined functions)

#include<stdio.h>
#include<string.h>
#include<conio.h>2
void concat(char[], char[]);
void compare(char[], char[]);
void reverse(char[]);
void length(char[]);
void main()
{
char s1[10],s2[10];
int i,opt,j;
clrscr();
l: printf("\n\nSelect any one of the given Options:\n");
printf("\n        Menu\n\n0.Length of the String\n1.String Reverse\n2.String Concatenation\n3.String Comparison\n4.Exit:\n");
scanf("%d",&opt);
switch(opt)
{
case 0:printf("Enter the string:");
       scanf("%s",s1);
       for(i=0;s1[i]!='\0';i++);
       printf("Length of the string is: %d characters",i);
break;
case 1:printf("Enter the string:");
       scanf("%s",s1);
       reverse(s1);
break;
case 2: printf("Enter 1st string:");
 scanf("%s",s1);
 printf("Enter 2nd string:");
 scanf("%s",s2);
 concat(s1,s2);
break;
case 3: printf("Enter 1st string:");
       scanf("%s",s1);
 printf("Enter 2nd string:");
       scanf("%s",s2);
 compare(s1,s2);
break;
case 4: exit(0);
default:printf("Choose the correct option\n");
}
goto l;
}
 void concat(char s1[], char s2[])
 {
 int i,j;
 i=strlen(s1);
 for(j=0;s2[j]!='\0';i++,j++)
 s1[i]=s2[j];

 s1[i]='\0';
 printf("Resultant String is: %s",s1);
 }
  void compare(char s1[], char s2[])
  {
   int i=0,flag;
   while(s1[i]!='\0'||s2[i]!='\0')
   {
   if(s1[i]==s2[i])
   {
   flag=0;
   }
   else
   {
   flag=1;
   break;
   }
   i++;
   }
   if(flag==0)
   printf("Both the Strings are Equal\n");
   else
   {
   printf("Given Strings are not Equal\n");
   }
   }
         void reverse(char s1[])
         {
         int i=0,j,temp;
         j=strlen(s1)-1;
    while(i<j)
    {
    temp=s1[i];
    s1[i]=s1[j];
    s1[j]=temp;
    i++;
    j--;
    }
    printf("Reverse of given string is: %s ",s1);
    }