How to find the length of a string without using library function strlen

/*How to find length of a string without using library function strstr.
How to use pointer/array to find length of string sentence. C++/CPP/C program/code to find length a string/word/sentence without using inbuilt function strlen.How to find the length of a string without using library function strlen*/

#include<stdio.h>

#include<string.h>

int strLen(char *p);

int main()

{

char arr1[20];

printf("Enter a String:\n");

scanf("%s",&arr1);

printf("You entered:%s\n",arr1);

int n;

n=strLen(arr1);

printf("Strlen of entered string is:%d\n",n);