string to int c

int isNumber(char s[])
{
    for (int i = 0; s[i]!= '\0'; i++)
    {
        if (isdigit(s[i]) == 0)
              return 0;
    }
    return 1;
}
atoi(str) is unsafe

This is the prefered method:
(int)strtol(str, (char **)NULL, 10)#include<string>
string str1 = "45"; 
string str2 = "3.14159"; 
string str3 = "31337 geek";

int myint1 = stoi(str1);
std::cout<<stoi(str1);