C++编译报错求助：‘arbitrage_two_diff_odds’未在此作用域声明

你遇到的‘arbitrage_two_diff_odds’ was not declared in this scope编译错误，核心原因是C++编译器要求函数在被调用前必须先被声明或定义。你的what_do_you_want_to_do函数里提前调用了arbitrage_two_diff_odds，但这个函数的定义在后面，编译器没法识别它。下面是具体的修复方案和代码优化建议：

1. 添加函数前置声明 #

在what_do_you_want_to_do函数定义之前，添加arbitrage_two_diff_odds的函数签名，让编译器提前知道这个函数的存在：

// 前置声明套利计算函数
double arbitrage_two_diff_odds(double a, double b, double c);

2. 修正main函数的调用错误 #

你的what_do_you_want_to_do函数设计上不需要传入参数，而且它返回double类型，不能直接赋值给int变量。修改main函数和what_do_you_want_to_do的函数签名：

// 调整函数签名，不需要传入参数
double what_do_you_want_to_do(){
    // ... 原有代码
}

int main() {
    what_do_you_want_to_do(); // 直接调用即可
    return 0;
}

3. 修复函数逻辑冗余 #

arbitrage_two_diff_odds函数里的else分支后重复输出了同一句提示，删掉重复的行：

// 原代码里的重复输出，保留一句即可
else 
    std::cout << "No profit for the odds entered, try different one again"<< std::endl;
// 删掉下面这句重复的
// std::cout << "No profit for the odds entered, try different one again"<< std::endl;

4. 补充函数返回值 #

C++要求非void类型的函数必须返回值，给arbitrage_two_diff_odds和what_do_you_want_to_do添加合适的返回值（比如返回计算后的利润，或者0表示执行完成）。

修改后的完整代码 #

/*Programm for making decision on arbitrage betting*/
#include <iostream>

// 前置声明套利计算函数
double arbitrage_two_diff_odds(double a, double b, double c);

// Prompting user to select an option.
double what_do_you_want_to_do(){
    double a, b, c;
    int z; // 把z的声明移到函数内部，不需要外部传入
    std::cout << "What do you want to do" << std::endl;
    std::cout << "For calculating Percentage & Profit for a single bet, PRES 1" << std::endl;
    std::cout << "For calculating Arbitrage Percentantage & Profit for two odds, PRESS 2" << std::endl;
    std::cout << "For calculating Arbitrage Percentantage & Profit for three odds, PRESS 3" << std::endl;
    std::cin >> z;

    //Using switch to branch.
    switch(z) {
        case 1:
            //call function 1，后续可以补充实现
            break;
        case 2:
            //call function 2
            arbitrage_two_diff_odds(a, b, c);
            break;
        case 3:
            //call function 3，后续可以补充实现
            break;
        default:
            std::cout << "Invalid option selected!" << std::endl;
            break;
    }
    return 0.0; // 返回一个默认值
}

//function for calculation of the arbitrage for two different odds.
double arbitrage_two_diff_odds(double a, double b, double c){
    //Prompting user for imput.
    std::cout << "Enter your values in this format \"1st odd, 2nd odd, investment\": ";
    std::cin >> a >> b >> c;

    //Calculating the sum of the percentage of the two different odds.
    double diff_two_odds = ((1/a)*100) + ((1/b)*100);

    //maniplation
    if (diff_two_odds <= 90) {
        double calc_profit = c/diff_two_odds;
        double idividual_bet1 = (c*((1/a)*100))/diff_two_odds;
        double idividual_bet2 = (c*((1/b)*100))/diff_two_odds;
        std::cout << "The arbitrage odds you put in are "<<a<< " and "<<b<<"."<< std::endl;
        std::cout << "The percentage gain for individual odd are "<<((1/a)*100)<<"% and "<<((1/b)*100)<<"% respectively."<<std::endl;
        std::cout << "The individual bet for your propose investment are "<<idividual_bet1<<"$ for "<<a<< " and "<<idividual_bet2<<"$ for " <<b<< " respectively, which equals "<<c<<"."<<std::endl;
        std::cout << "From your proposed investment of "<<c<<"$, Your arbitrage profit is "<<calc_profit<< std::endl;
        return calc_profit; // 返回计算出的利润
    } else {
        std::cout << "No profit for the odds entered, try different one again"<< std::endl;
        return 0.0; // 无利润时返回0
    }
}

int main() {
    what_do_you_want_to_do();
    return 0;
}

额外提示 #

• 后续可以补充实现case 1和case 3对应的函数，同样要注意前置声明
• 可以添加输入验证，比如确保用户输入的赔率和投资金额是正数，避免除以0的错误

内容的提问来源于stack exchange，提问作者Paschal