How to use nested ternary operators in C++

Question

I am trying to use nested ternary operators using following code, but it is giving wrong answer, I am not getting what's the mistake is.

#include <iostream>
using namespace std;
int main()
{
cout<<"Hello World\n";
int age, Result ;
cout<<"Enter age:";
cin>>age;

Result=age<0?-1
        :0<=age<=10?0
        :11<=age<=18?1
        :-2;
cout<<"Result is: "<<Result;

return 0;
}

For the input age 13 its giving Result as 0 and for input age 20 also its giving result as 0. I am not getting what's the mistake. Could you help me? Thank you.

`warning C4804: '<=': unsafe use of type 'bool' in operation` — Retired Ninja, Jan 24 '18 at 01:25

score 3 · Accepted Answer · answered Jan 24 '18 at 01:23

3

0<=age<=10 is not doing what you think it is.

Let's say you enter an age of 11. This snippet will run the check 0 <= age, which is true since age is 11. Then it will check true <= 10. True gets cast into an integer, so the check is 1 <= 10, which is true, so your ternaries will return 0.

Change the ternaries to:

Result=                 (age < 0) ? -1
        : ((0<=age) && (age<=10)) ? 0
        :((11<=age) && (age<=18)) ? 1
        :       /*else*/           -2;

answered Jan 24 '18 at 01:23

scohe001

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3

You can simplify to `int Result = age < 0 ? -1 : age <= 10 ? 0 : age <= 18 ? 1 : -2;` if you like. – Retired Ninja Jan 24 '18 at 01:29
@RetiredNinja +1, fair point. I'd edit it in, but the question is closed so I won't bother to edit further. – scohe001 Jan 24 '18 at 01:31
None of those parentheses are needed. – Pete Becker Jan 24 '18 at 01:40
Always good to know both ways since the shortest code isn't always the most readable, and if you wanted to select [1-9], [11-19], etc. you'd need both ends of the range. – Retired Ninja Jan 24 '18 at 01:42
Thank you @scohe001 and Retired Ninja – R June Jan 24 '18 at 01:51

How to use nested ternary operators in C++

1 Answers1