Question

//Writing a letter

#include <iostream>
using namespace std;

int main() {
string first_name;      //Name of addressee
string friend_name;     //Name of a friend top be mentioned in the letter
char friend_sex, m, f;  //variable for gender of friend

friend_sex = 0;

cout << "\nEnter the name of the person you want to write to: ";
cin >> first_name;

cout << "Enter the name of a friend: ";
cin >> friend_name;

cout << "Enter friend's sex(m/f): ";    //Enter m or f for friend
cin >> friend_sex;                      //Place m or f into friend_sex

cout << "\nDear " << first_name << ",\n\n"
     << "   How are you? I am fine. I miss you!blahhhhhhhhhhhhhhhh.\n"   
     << "blahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh.\n"
     << "Have you seen " << friend_name << " lately? ";

//braces only necessary if there are more than one statement in the if function
if(friend_sex == m) {
    cout << "If you see " << friend_name << ", please ask him to call me.";             
}   //If friend is male, output this
if(friend_sex == f) {
    cout << "If you see " << friend_name << ", please ask her to call me.";
}   //If friend is female, output this

return(0);
}

实际上是这样：

Enter the name of the person you want to write to: MOM

Enter the name of a friend: DAD

Enter friend's sex(m/f): m

Dear MOM, 

        How are you? I am fine. I miss you! blahhhhhhhhhhhhhhhhh.
        blahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh.
        Have you seen DAD lately?

这个程序正在模拟一个简短的字母。输出一个单词块很容易，但是当我想要一些条件放在字母中时，我遇到了麻烦。即使我在程序问我时输入了friend_sex（m / f），if语句的输出也没有实现。为什么呢？

Answer 1

您正在针对未初始化的字符变量friend_sex测试m。您可能希望针对文字值'm'进行测试。这就像有一个名为seven的整数变量，并期望它保持值7。

Answer 2

char m, f

这声明了名为m和f的变量。这里m和f是变量名，而不是值'm'和'f'。现在他们正在包含垃圾值。

您需要初始化它们：

char m = 'm', f = 'f'

或者你可以将char常量直接放在if语句中，而不是使用变量m，f。

if (friend_sex == 'm') {}

Answer 3

你检查了未初始化的friend_sex aginst m和f。你可以检查文字'm'或'f'

Answer 4

您正在将friend_sex与未初始化的变量m进行比较。您应该将它与常量'm'进行比较。请注意单引号。

Answer 5

您需要检查if (friend_sex == 'm')之类的内容，而不是根据变量m进行检查。基本上你需要检查预期值。

Answer 6

这是你的问题：

if(friend_sex == m)

您要比较两个变量，而不是您放入friend_sex变量的内容。

所以如果你改成它：

if(friend_sex == 'm')

现在，这将检查friend_sex的内容是否为'm'。

C ++ If语句不起作用

6 个答案: