C++基础货币转换器仅USD转英镑生效，其他币种转换失效求助

核心错误原因 #

你的代码里所有判断货币类型的地方都用了<=来比较字符串，这是完全错误的。C++中字符串的<=是按字典序（字母顺序）比较，不是判断是否相等。比如：

• "Euro" 的字典序比 "Usd"、"Pound"、"Peso" 都小，所以当你输入s = "Euro"时，s <= Euro、s <= Usd、s <= Pound、s <= Peso都会返回true，导致多个外层if块同时执行，逻辑彻底混乱。
• 只有USD转英镑碰巧生效，是因为字典序的巧合让对应条件刚好符合，但这完全是偶然。

修复后的完整代码 #

#include <iostream>
#include <string>

using namespace std;

int main()
{
    const string Euro = "Euro";
    const string Usd = "Usd";
    const string Pound = "Pound";
    const string Peso = "Peso";

    string from_currency;
    string to_currency;
    float amount;
    float converted_amount;

    cout << "请选择要转换的货币类型：Usd,Euro,Pound,Peso" << endl;
    cin >> from_currency;
    
    cout << "请选择转换目标货币：" << endl;
    cin >> to_currency;

    cout << "请输入" << from_currency << "的金额：" << endl;
    cin >> amount;

    // 欧元转其他货币
    if (from_currency == Euro) 
    {
        if (to_currency == Usd) {
            converted_amount = amount * 1.02;
            cout << "转换后金额：" << converted_amount << " 美元" << endl;
        }
        else if (to_currency == Pound) {
            converted_amount = amount * 0.85;
            cout << "转换后金额：" << converted_amount << " 英镑" << endl;
        }
        else if (to_currency == Peso) {
            converted_amount = amount * 131.82;
            cout << "转换后金额：" << converted_amount << " 比索" << endl;
        }
        else {
            cout << "不支持的目标货币类型" << endl;
        }
    }
    // 美元转其他货币
    else if (from_currency == Usd) 
    {
        if (to_currency == Euro) {
            converted_amount = amount / 1.02;
            cout << "转换后金额：" << converted_amount << " 欧元" << endl;
        }
        else if (to_currency == Pound) {
            converted_amount = amount / 1.2;
            cout << "转换后金额：" << converted_amount << " 英镑" << endl;
        }
        else if (to_currency == Peso) {
            converted_amount = amount * 129.07;
            cout << "转换后金额：" << converted_amount << " 比索" << endl;
        }
        else {
            cout << "不支持的目标货币类型" << endl;
        }
    }
    // 英镑转其他货币
    else if (from_currency == Pound) 
    {
        if (to_currency == Usd) {
            converted_amount = amount * 1.2;
            cout << "转换后金额：" << converted_amount << " 美元" << endl;
        }
        else if (to_currency == Euro) {
            converted_amount = amount * 1.18;
            cout << "转换后金额：" << converted_amount << " 欧元" << endl;
        }
        else if (to_currency == Peso) {
            converted_amount = amount * 154.92;
            cout << "转换后金额：" << converted_amount << " 比索" << endl;
        }
        else {
            cout << "不支持的目标货币类型" << endl;
        }
    }
    // 比索转其他货币
    else if (from_currency == Peso) 
    {
        if (to_currency == Usd) {
            converted_amount = amount * 0.0077;
            cout << "转换后金额：" << converted_amount << " 美元" << endl;
        }
        else if (to_currency == Pound) {
            converted_amount = amount * 0.0065;
            cout << "转换后金额：" << converted_amount << " 英镑" << endl;
        }
        else if (to_currency == Euro) {
            converted_amount = amount * 0.0076;
            cout << "转换后金额：" << converted_amount << " 欧元" << endl;
        }
        else {
            cout << "不支持的目标货币类型" << endl;
        }
    }
    else {
        cout << "不支持的源货币类型" << endl;
    }

    return 0;
}

关键修复点 #

• 把所有字符串比较的<=替换为==，正确判断货币类型是否匹配。
• 外层条件用else if替代独立的if，确保每次只有一个货币转换逻辑块执行，避免多个块同时触发。
• 内层条件也改用else if，并增加错误提示，处理用户输入无效货币的情况。
• 修正了非标准的void main()为标准的int main()，并添加return 0;符合C++规范。
• 变量名更具可读性（比如s改为from_currency，c改为to_currency），方便后续维护。

内容的提问来源于stack exchange，提问作者Flame