How can I make a case statement based on an iterable?

Question

I want to make a case statement based on an iterable, but I understand that the case expression must be a constant. What is a workaround for this?

I tried the below code, but it still does not work.

#include <iostream>
using std::cout;
using namespace std;

int main()
{
    int i = 0;
    while( i >= 0)
    {
        const int z = i;
        cout << "Enter a number other than " << z << "!\n";
        int choice;
        cin >> choice;
        switch(choice){
            case z: cout << "Hey! you weren't supposed to enter "<< z <<"!"; return 0; break;
            default: if(i==10)
                    {
                        cout << "Wow, you're more patient then I am, you win."; return 0;
                    }
                    break;
        }
        i++;
    }

}

It's totally impossible with switch-case, because you have to give value known at compile time for case. Use `if {} else if {} else {}` pattern instead — Garf365, Oct 19 '17 at 14:33
`switch()` with one case is not more readable than `if else` anyway. — Slava, Oct 19 '17 at 14:36

score 6 · Accepted Answer · answered Oct 19 '17 at 14:35

6

case requires constant integral values known at compile-time.

So you'll have to use if-s:

if (choice == z) {
  cout << "Hey! you weren't supposed to enter "<< z <<"!";
  return 0;
} else if (i == 10) {
  cout << "Wow, you're more patient then I am, you win.";
  return 0;
}

answered Oct 19 '17 at 14:35

Daniel Trugman

8,186
20
41

if, else sounds like the only option. I can remove z and just work with i now too. Thanks! – J. Smith Oct 19 '17 at 15:14

score 0 · Answer 2 · answered Oct 19 '17 at 15:19

When a switch statement is encountered, the execution continues from from the corresponding case block all the way to the end of the switch statement unless a break is encountered. Therefore the switch statement is closer in "spirit" with an goto statement and not nested ifs. The implementation is also different and it is done using assembly branch tables as explained here.

Why can't I use non-integral types with switch

Therefore, like Daniel Trugman said you need to use nested if statements.

How can I make a case statement based on an iterable?

2 Answers2