為什么“ else”語句出現在輸出中？

Question

我是C ++的新手，當我遇到問題時正在嘗試使用該程序。 那不是技術性的。 該程序運行正常。

#include<iostream>    
int main()
{
    using namespace std;
    int num1, num2;
    char ch;
    cout << "Enter the two integers: ";
    cin >> num1 >> num2;
    cout << "Choose one of the following arithmetic operators: " << endl;
    cout << "+" << endl;
    cout << "-" << endl;
    cout << "*" << endl;
    cout << "/" << endl;
    cin >> ch;
    if (ch == '+')
        cout << "The sum of the two numbers is: " << num1 + num2 << endl;
    if (ch == '-')
        cout << num2 << " subtracted from " << num1 << " is " << num1 - num2 << endl;
    if (ch == '*')
        cout << "When multiplied: " << num1*num2 << endl;
    if (ch == '/')
        cout << num1 << " divided by " << num2 << " will be " << num1 / num2 << endl;
    else
        cout << "Wrong input. Try again.";
    return 0;
}

現在是問題所在。 當滿足if語句以及提供的計算時，輸出還將顯示else語句中的語句。 我嘗試將else編輯為：-

else if(ch=!'+','-','*','/')

和

if(ch=!'+','-','*','/')

但它們似乎都不起作用。 在所有情況下，“輸入錯誤。請重試。” 不知何故找到了輸出的方式。 我要去哪里錯了？

Answer 1

您的整個結構必須為if - else if - else ，如下所示：

if(ch=='+')
    cout<<"The sum of the two numbers is: "<<num1+num2<<endl;
else if(ch=='-')
    cout<<num2<<" subtracted from "<<num1<<" is "<<num1-num2<<endl;
else if(ch=='*')
    cout<<"When multiplied: "<<num1*num2<<endl;
else if(ch=='/')
    cout<<num1<<" divided by "<<num2<<" will be "<<num1/num2<<endl;
else 
    cout<<"Wrong input. Try again.";

但這是做事的最好方法嗎？ 可能不是。 由於您只是在測試以查看ch等於什么，因此實際上可以使用另一個內置的C ++構造，即switch語句：

switch (ch) {
  case '+':
    cout << "The sum of the two numbers is: " << num1+num2 << endl;
    break;
  case '-':
    cout << num2 << " subtracted from " << num1 << " is " << num1-num2 << endl;
    break;
  case '*':
    cout << "When multiplied: " << num1*num2 << endl;
    break;
  case '/':
    cout << num1 << " divided by " << num2 << " will be " << num1/num2 << endl;
    break;
  default:
    cout << "Wrong input. Try again." << endl;
    break;
}

Answer 2

在您的原始代碼中， else僅適用於最后的if語句。 您需要鏈接您的條件：

if(ch=='+')
    cout<<"The sum of the two numbers is: "<<num1+num2<<endl;
else if(ch=='-')
    cout<<num2<<" subtracted from "<<num1<<" is "<<num1-num2<<endl;
else if(ch=='*')
    cout<<"When multiplied: "<<num1*num2<<endl;
else if(ch=='/')
    cout<<num1<<" divided by "<<num2<<" will be "<<num1/num2<<endl;
else 
    cout<<"Wrong input. Try again.";

但是，最好使用switch語句：

switch (ch) {
case '+':
    cout<<"The sum of the two numbers is: "<<num1+num2<<endl;
    break;
case '-';
    cout<<num2<<" subtracted from "<<num1<<" is "<<num1-num2<<endl;
    break;
case '*':
    cout<<"When multiplied: "<<num1*num2<<endl;
    break;
case '/':
    cout<<num1<<" divided by "<<num2<<" will be "<<num1/num2<<endl;
    break;
default:
    cout<<"Wrong input. Try again."; 
}

Answer 3

當ch不等於/時， else部分將始終執行，因為else部分僅與if(ch=='/')匹配。可能要使用if else梯形圖或切換大小寫。

Answer 4

“其他語句”與最后的“如果語句”鏈接。 因此，如果非最后一個if語句變為true，則最后一個if語句變為false，這意味着對else語句的真實評價。 您可以將if語句更改為“ else if”（不要修改第一個if語句）。