需要非常简单的C ++ for循环帮助

Question

for( int i = 0; i <= 10; i++ )
{
    cout << setw(2) << i << setw(10) << ( i <= 5 ? cout <<" = Chipotle" : cout << " = McDonalds" ) << endl;
}

So, I expected the output to be:

 0 = Chipotle
 1 = Chipotle
 2 = Chipotle
 3 = Chipotle
 4 = Chipotle
 5 = Chipotle
 6 = McDonalds
 7 = McDonalds
 8 = McDonalds
 9 = McDonalds
10 = McDonalds

(Don't worry about the setw formatting)

Instead, my IDE gave me:

 = Chipotle 0  0x602208                                                                                                             
 = Chipotle 1  0x602208                                                                                                             
 = Chipotle 2  0x602208                                                                                                             
 = Chipotle 3  0x602208                                                                                                             
 = Chipotle 4  0x602208                                                                                                             
 = Chipotle 5  0x602208                                                                                                             
 = McDonalds 6  0x602208                                                                                                            
 = McDonalds 7  0x602208                                                                                                            
 = McDonalds 8  0x602208                                                                                                            
 = McDonalds 9  0x602208                                                                                                            
 = McDonalds10  0x602208

Where did I went wrong?

Answer 1

你显示cout本身，删除三元运算符中的cout ：

cout << setw(2) << i << setw(10) << ( i <= 5 ? " = Chipotle" : " = McDonalds" ) << endl

Answer 2

You are trying to cout a cout.

( i <= 5 ? cout <<" = Chipotle" : cout << " = McDonalds" )

becomes either

cout <<" = Chipotle" 
//or 
cout << " = McDonalds"

So you are trying to do

cout << setw(2) << i << setw(10) << cout <<" = Chipotle" 
//or
cout << setw(2) << i << setw(10) << cout <<" = McDonalds" 

Which is incorrect. You need to change you code to

( i <= 5 ? " = Chipotle" : " = McDonalds" )

Which will expand to

cout << setw(2) << i << setw(10) << " = Chipotle" 
//or
cout << setw(2) << i << setw(10) << " = McDonalds" 

Answer 3

When i <= 5 is true, this

cout << i << ( i <= 5 ? cout <<" = Chipotle" : cout << " = McDonalds" ) << endl

evaluates like this:

cout << i << (cout << " = Chipotle") << endl

I omitted the setw manipulators here to make the code easier to read, which would affect spacing in the result but makes no difference otherwise. The result is the same as this sequence of operations:

cout << " = Chipotle"; // the thing in `()` gets evaluated first
cout << i;
cout << cout; // because (cout << " = Chipotle") evaluates to cout
cout << endl;

which is exactly what you see for the first few lines. cout itself is printed out as 0x602208 . After that you get McDonalds instead of Chipotle .

If you just write cout once, at the left end of your output expression, you will get the output you want.

Answer 4

You do not have to write cout again inside the if condition you have written using the ?: operators. Just place the string what you want to print without the cout

Answer 5

This is more precise and readable approach.

for( int i = 0; i <= 10; i++ )
{
    cout << setw(2) << i << setw(10) ;
    if(i<= 5)
    {
        cout <<" = Chipotle"<<endl;
    }
    else
    {
        cout << " = McDonalds" << endl;
    }
}