Use of case without switch, please explain the output of this code

user_13308018 0
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We use cases with switch. But here the cases are inside the default case, so it should require one more switch. But the code doesn't give any compile time errors.

#include<iostream>
int main()
{
    int num=4;
    while (num)
    {
        switch(num)
        {

            default:
                case 1:
                    std::cout<<"Executing "<<num<<"\n";
                
                case 2:
                
                case 3:
    
                break;
        }
        num--;          
    }
    return 0;
}

Moreover the output is Executing 4 and then Executing 1. According to me the output should be Executing 1 because each time default is being entered. It will enter case 1 when value is 1. But first please explain how this is compiling, because according to me there should be a nested switch.

switch-statement c++
2 Answers

In a switch, all case and default are at the same level, you were just caught by the (stupid?) indentation, and a rather inconsistent use of default. In fact it should read:

    switch(num)
    {
            default:
            case 1:
                std::cout<<"Executing "<<num<<"\n";
            
            case 2:
            case 3:
                break;
    }

Meaning: do nothing (break) if 2 or 3, and display Executing ... for 1 or any other value.

This would do the same and would be IMHO more readable:

    switch(num)
    {
        case 2:
        case 3:
            break;

        default:
            std::cout<<"Executing "<<num<<"\n";
    }
user_35452730

case 1 to 3 are indented wrongly.

It's a so-called "fallthrough". If the switch hits the default case, it will fall through until it reaches a break meaning it will execute other cases on the way.
In your case, if it hits the default case, it will execute case 1, case 2 and case 3

Edit: I recommend ending each case with a break and putting default as the last case. Only if you really want to fallthrough and know what you do you could omit the break.

user_30011500
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