C++程序选项选择异常：无论选何选项均触发同一结果求助

我基于《小屁孩日记》编写了一款C++程序，玩家扮演Greg的父亲，有3种处置Greg的可选操作，但运行时无论选第一个还是第三个选项，程序始终只执行第一个选项的输出逻辑。原代码如下：

#include <iostream>

using namespace std;

void greg(int choice){
    cout<<"Option 1: Scold."<<endl;
    cout<<"Option 2: Take away games."<<endl;
    cout<<"Option 3: kill "<<endl;
    cin>>choice;
    //Options on what to do with greg and getting user input.
    if(choice = '1'){
    cout<<"You told Greg he sucks. Responds with:"<<endl;
    cout<<"Ok.."<<endl; 
    } else if(choice = '2'){
    cout<<"You storm into Greg's room while Greg keeps asking you why."<<endl;
    cout<<"Once you are insde and grab his game."<<endl;    
    }else if(choice = '3'){
    cout<<"you killed greg."<<endl;
    cout<<"A white bang then proceeds to happen."<<endl;
    cout<<"You killed the main character. You no longer exist."<<endl;  
        }else{
        cout<<"no"<<endl;   
            }
}
//All above is what will happen if you pick a choice.
int main()
{
    cout<<"There once was a guy named Frank."<<endl;
    cout<<"You talk to greg."<<endl;
    cout<<"Yeah dad?"<<endl;
    greg(3);
    return 0;
}

问题根源 #

• 赋值/比较运算符混淆：所有if判断里用的是=（赋值运算符），而不是==（比较运算符）。choice = '1'会把字符'1'的ASCII值（49）赋给choice，这个表达式的结果为非零，C++里会判定为true，导致第一个if分支永远触发，后面的分支根本不会执行。
• 类型不匹配：choice是int类型，但你用字符'1'/'2'/'3'来比较，虽然能自动转换，但逻辑上不严谨。

修复后的代码 #

#include <iostream>

using namespace std;

void greg(){
    int choice;
    cout<<"Option 1: Scold."<<endl;
    cout<<"Option 2: Take away games."<<endl;
    cout<<"Option 3: kill "<<endl;
    cin>>choice;
    //Options on what to do with greg and getting user input.
    if(choice == 1){
        cout<<"You told Greg he sucks. Responds with:"<<endl;
        cout<<"Ok.."<<endl; 
    } else if(choice == 2){
        cout<<"You storm into Greg's room while Greg keeps asking you why."<<endl;
        cout<<"Once you are inside and grab his game."<<endl;    
    }else if(choice == 3){
        cout<<"you killed greg."<<endl;
        cout<<"A white bang then proceeds to happen."<<endl;
        cout<<"You killed the main character. You no longer exist."<<endl;  
    }else{
        cout<<"no"<<endl;   
    }
}
//All above is what will happen if you pick a choice.
int main()
{
    cout<<"There once was a guy named Frank."<<endl;
    cout<<"You talk to greg."<<endl;
    cout<<"Yeah dad?"<<endl;
    greg();
    return 0;
}

修复说明 #

1. 把所有if条件里的=替换成==，实现正确的条件判断。
2. 将比较值从字符'1'改为整数1，和choice的int类型匹配。
3. 移除greg函数的参数choice——原参数会被输入值覆盖，完全多余，直接在函数内部定义int choice更合理。

内容的提问来源于stack exchange，提问作者popsicle7