include for atoi code example

Example 1: atoi

#include <stdlib.h> //atoi's library
#include <stdio.h>

int main (void)
{
	string input = "9";
  
  	int output = atoi(input);
  
  	printf("%i", output);
  
  	//this will print out 9 as an int not a string
}

Example 2: what is atoi in strinf

The C library function int atoi(const char *str) converts the 
string argument str to an integer (type int).

Note: It is used in case of string because in strings a number is
also stored as char  and we have to do Typecasting  form (string -> int)