[ CPP ] find if char * is numeric

is_numeric.cpp

#include <cctype>

bool stringutils::isNum(char *s) {
    int i = 0,  flag;

    while(s[i]){
            //if there is a letter in a string then string is not a number
        if(isalpha(s[i])){
            flag = 0;
            break;
        }
        else flag = 1;
        i++;
        }
    if (flag == 1) return true;
    else return false;
}