[2018年4月28号]C++ primer 课后练习第九章顺序容器第十章泛型算法-优快云博客

本文介绍如何使用C++将字符串转换为整数或浮点数，并实现了一个简单的表达式解析器，能够处理加法运算。此外，还提供了一个日期解析类，用于从字符串中提取日期信息。

9.50

int main() {
    vector<string > vecStr = {"12","3","4","5"};
    int theSum = 0;
    for(auto str:vecStr){
        int tmpInt = stoi(str);
        theSum += tmpInt;
    }

    cout<< theSum << endl;
    for (;;);
    return 0;
}

int main() {
    vector<string > vecStr = {"12.1","3.2","4.3","6.5"};
    float theSum = 0;
    for(auto str:vecStr){
        float tmpInt = stof(str);
        theSum += tmpInt;
    }

    cout<< theSum << endl;
    for (;;);
    return 0;
}

9.51

Date::Date(const string& str) {
    const string numbers = "0123456789";
    int number_begin = 0;
    int number_end = 0;
    number_begin = str.find_first_of(numbers, number_begin);
    number_end =   str.find_first_not_of(numbers, number_end);
    string dayStr(str, number_begin, number_end - number_begin);
    day = stoi(dayStr);
    number_begin++;
    number_end++;
    number_begin = str.find_first_of(numbers, number_begin);
    number_end = str.find_first_not_of(numbers, number_end);
    string monthStr(str, number_begin, number_end - number_begin);
    month = stoi(monthStr);
    number_begin++;
    number_end++;
    number_begin = str.find_first_of(numbers, number_begin);
    number_end = str.find_first_not_of(numbers, number_end);
    if(number_end == string::npos){
        number_end = str.size();
    }
    string yearStr(str, number_begin, number_end - number_begin);
    year = stoi(yearStr);
}

9.51

class Date {
public:
    Date() = default;
    Date(const string&) ;
    int year;
    int month;
    int day;
};

Date::Date(const string& str) {
    const string numbers = "0123456789";
    int number_begin = 0;
    int number_end = 0;
    number_begin = str.find_first_of(numbers, number_begin);
    number_end =   str.find_first_not_of(numbers, number_end);
    string dayStr(str, number_begin, number_end - number_begin);
    day = stoi(dayStr);
    number_begin++;
    number_end++;
    number_begin = str.find_first_of(numbers, number_begin);
    number_end = str.find_first_not_of(numbers, number_end);
    string monthStr(str, number_begin, number_end - number_begin);
    month = stoi(monthStr);
    number_begin++;
    number_end++;
    number_begin = str.find_first_of(numbers, number_begin);
    number_end = str.find_first_not_of(numbers, number_end);
    if(number_end == string::npos){
        number_end = str.size();
    }
    string yearStr(str, number_begin, number_end - number_begin);
    year = stoi(yearStr);
}

9.52

仅以加法为例

int getSum (const string& left, const string& right){
    return stoi(left) + stoi(right);
}

int main() {
    string theExpression = "1+(2+3)+4";
    stack<string > sta;
    int meet = 0;
    for(auto tmp : theExpression){
        if(tmp == '('){
            meet = 1;
        }
        if (tmp == ')') {
            sta.push(string(1, tmp));
            meet = 0;
        }
        if(meet){
            sta.push(string(1, tmp));
        }
    }

    string left, right, symbol;
    
    int popState = 0;
    while (!sta.empty())
    {
        if(sta.top().find(" ") != string::npos){
            sta.pop();
            continue;
        }
        if(sta.top().find_first_of("0123456789") == string::npos){
            if (sta.top() != "(" && sta.top() != ")") {
                symbol+= sta.top();
            }
            sta.pop();
            popState++;
            continue;
        }
        if(popState == 1){
            right += sta.top();
        }
        if(popState == 2){
            left += sta.top();
        }
        sta.pop();
    }
    if(symbol == "+"){
        sta.push(to_string(getSum(left,right)));
    }
    cout << sta.top() << endl;
    for (;;);
    return 0;
}