Question

只是制作一个小程序来开始c ++，并且编译器说有一个没有if引用于while中的while循环，但显然并非如此，我不明白为什么。如果我删除while循环，它可以正常工作。

#include <iostream>
using namespace std;

int number;

int arithmetic(int num)
{
 if(num > 20)
  num = num * 5;
 else 
  num = 0;
 return (num);
}

int main()
{ 
 int wait;
 cout <<  "I will take any number providing it is higher than twenty" << endl;
 cout <<  "and I will multiply it by 5. I shall then print every number" << endl;
 cout <<  "from that number backwards and say goodbye." << endl; 
 cout <<  "Now please give me your number: " << endl;
 cin >> number;
 int newnum = arithmetic(number);
 if (newnum != 0)
  cout << "Thank you for the number, your new number is" << newnum << endl;
  while(newnum > 0){
   cout << newnum;
   --newnum;
  }
  cout << "bye";
 else
  cout << "The number you entered is not greater than twenty";
 cin >> wait;
 return 0;
}

Answer 1

你缺少括号。

if (newnum != 0)
cout << "Thank you for the number, your new number is" << newnum << endl;
while(newnum > 0){
cout << newnum;
--newnum;
 }
cout << "bye";
else
cout << "The number you entered is not greater than twenty";

虽然你应该：

if (newnum != 0)
{
   cout << "Thank you for the number, your new number is" << newnum << endl;
   while(newnum > 0){
   cout << newnum;
   --newnum;
   cout << "bye";
}
else
    cout << "The number you entered is not greater than twenty";

如果if语句中有多个操作，则应始终使用括号。如果你只有一个，你也可以省略它们（如在“其他”声明中）。

Answer 2

{之前需要if (newnum != 0)，}之前需要else。

Answer 3

这种结构是错误的：

if(something)
  line1;
  line2; // this ; disconnects the if from the else
 else 
  // code

你需要像

这样的东西

if ( something ) {
  // more than one line of code 
} else  {
  // more than one line of code
}

c ++错误：否则没有先前的if

3 个答案: