NEED ATOI HELP

[joegrizzly]

hey,I'm in my first programming class and i cant figure out how to use atoi to change from a string to an integer.
please let me know what i'm doing wrong!!!!

#include <iostream>
#include <string>
using namespace std;
int main()
{
int num; 
string digits= "153";
num = atoi(digits.c_str());
cout<<num<<endl;

}

[j3Rz8vqX]

include the <cstdlib>

[joegrizzly]

still got errors. using microsoft visual c++ 2010 express if it matters

[j3Rz8vqX]

I'm on gcc 4.7.1, no errors with the code below:

#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;
int main()
{
    int num;
    string digits= "153";
    num = atoi(digits.c_str());
    cout<<num<<endl;
}

Output was:

153