atoi

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

//CONVERT STRING TO INT

int main () {
   int val;
   char str[20];
   
   strcpy(str, "98993489");
   val = atoi(str);
   printf("String value = %s, Int value = %d\n", str, val);

   strcpy(str, "tutorialspoint.com");
   val = atoi(str);
   printf("String value = %s, Int value = %d\n", str, val);

   return(0);
}string s;

int i = atoi(s.c_str());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)