How can I replace this code with one if statement?

Question

For the sake of challenge, how can I replace this code with only one if statement?

unsigned int x, y;
cin>>x;
if((x>=0)&&(x<=1)) y = 1;
else if (x<=3) y = 2;
    else if(x<=5) y = 3;
        else y = 6;

Why are you trying to get it to one `if` statement? Readability? Performance? Challenge? — blackbrandt, Sep 20 '21 at 12:39
There is not a clean way to do that. Maybe a better question is: why do you *want* to replace that code with a single `if`? — 0x5453, Sep 20 '21 at 12:39
Challange, maybe I can replace all of that with the Conditional operator ‘?’, but I can't find a solution. — Alexander, Sep 20 '21 at 12:42
@Alexander next time consider posting code challenges on https://codegolf.stackexchange.com/ instead ;) — Jan Hohenheim, Sep 20 '21 at 13:02
@JanHohenheim from the `puzzle` tag description: "DO NOT USE - prefer constructive questions, or use more descriptive tags" — 463035818_is_not_an_ai, Sep 20 '21 at 13:15
...Otherwise, your question might be appropriate for CodeGolf. — 463035818_is_not_an_ai, Sep 20 '21 at 13:16
look mum, no divs ;) ```static int value[6]={1,1,2,2,3,3}; y=(x<=5) ? value[x] : 6;``` — Pepijn Kramer, Sep 20 '21 at 14:29
@463035818_is_not_a_number yep, hence my last comment to the question — Jan Hohenheim, Sep 21 '21 at 14:03

score 2 · Answer 1 · answered Sep 20 '21 at 12:44

Make a table of inputs and outputs:

0 — 1
1 — 1
2 — 2
3 — 2
4 — 3
5 — 3
Other — 6

Now make a logical expression which distinguishes specific inputs from "others".

x ≥ 0 and x ≤ 5

(note: for unsigned type you can remove the comparison with 0)

Now make a formula which calculates given outputs from given inputs:

x / 2 + 1

Jan Hohenheim · Accepted Answer · 2021-09-23T12:34:53.130

Without knowing why you want to use a single if, it's hard to tell. Of course, you can use ternary operators without any ifs:

unsigned int x, y;
cin>>x;
y = x<=1
? 1
: x<=3 
    ? 2
    : x<=5
      ? 3
      : 6;

Or ugly boolean casting hacks for exactly one if (please don't actually do this outside of a puzzle or codegolf context):

unsigned int x, y;
cin>>x;
if (x<=5) {
    y = 1 + (int)(x == 2 || x == 3) + (int)(x == 4 || x == 5);
} else {
    y = 6;
}

Or, if you insist on exactly one if:

unsigned int x, y;
cin>>x;
if (x <= 5) {
   y = x/2 + 1;
} else {
   y = 6;
}

@Pietrek's answer shows you the better variant with a ternary operator (slightly modified here):

unsigned int x, y;
cin>>x;
auto const cutoff = 6;
y = x < cutoff ? x/2 + 1 : cutoff;

Note that in any case x >= 0 is always true when working with unsigned data types, so I omitted it.

If this is not purely a puzzle challenge but actual production code, please use the last example and make the number 6 a const or constexpr with a meaningful name.

The version with `min` doesn't work for x = 6 – anatolyg Sep 20 '21 at 13:04 — anatolyg, Sep 20 '21 at 13:04
@anatolyg good catch! Gonna fix it – Jan Hohenheim Sep 23 '21 at 12:24 — Jan Hohenheim, Sep 23 '21 at 12:24

score 0 · Answer 3 · answered Sep 20 '21 at 12:51

0

y = x <= 5 ? x / 2 + 1 : 6;

answered Sep 20 '21 at 12:51

Pietrek

66
6

How can I replace this code with one if statement?

3 Answers3