Expression evaluation Basic Calculator

int calculate(string s) {
    int total = 0;
    vector<int> signs(2, 1);
    for (int i=0; i<s.size(); i++) {
        char c = s[i];
        if (c >= '0') {
            int number = 0;
            while (i < s.size()  &&  s[i] >= '0')
                number = 10 * number + s[i++] - '0';
            total += signs.back() * number;
            signs.pop_back();
            i--;
        }
        else if (c == ')')
            signs.pop_back();
        else if (c != ' ')
            signs.push_back(signs.back() * (c == '-' ? -1 : 1));
    }
    return total;
}

• https://leetcode.com/problems/basic-calculator/discuss/
• http://www.cnblogs.com/grandyang/p/4570699.html
• http://www.geeksforgeeks.org/expression-evaluation/
• http://blog.csdn.net/nicaishibiantai/article/details/45740649