Write C program example to find length of Given String

Write C program to find length of  Given String  using call by reference, Write C program to find length of  Given String  using call by reference with source code, Write C program to find length of  Given String  using pointer with source code,Write C program using function to find length of  Given String  using call by reference

#include<stdio.h>

#include<conio.h>

void len(char *,int *);

void main()

{

 char s[100],*ptr;

 int l,*le;

 le=&l;

 printf("Enter the string :  \t");

 gets(s);

 ptr=s;

 len(ptr,&le);

 printf("length=%d",le);

 getch();

 }

void len(char *a,int *l)

{

int i=0;

 while(*a!='\0')

 {

  i++;

  a++;

 }

 *l=i;

}