Converting if-else to for loop

Question

int max_range = 100;
// I do not want to add more else if.. Actually max range is still 100 with more else ifs.
// Range can take values from 0 to 100

if (range <= 10){
    a[0]= value;
}

else if (range > 10 && range <= 20){
    a[1]= value;
}

else if (range> 20 && range <= 30){
    a[2]= value;
}

else if (range > 30 && range <= 40){
    a[3]= value;
}

else if (range> 40 && <= max_range){
    a[4]= value;
}

It is simple code. I would like it to remove the nested else if's and use a for loop. How can I convert this into a for loop?

if-else is one operation - what is your for loop going to loop round? — doctorlove
– doctorlove, Commented Sep 26, 2017 at 11:42
I don't really see how you could replace it with a loop. You could loop over the index into a I guess, but then you would still need some kind of condition for the range anyway. Would it be more readable and easier to understand? Probably not. — Some programmer dude
– Some programmer dude, Commented Sep 26, 2017 at 11:43
Changing if to switch is something I've seen, but it looks like you can make a loop that goes from 0 to max_range / 10. The loop value (say i) could be used as an index, like if (range > i*10 && range <= i*10+10){ a[i] = value; }. — GolezTrol
– GolezTrol, Commented Sep 26, 2017 at 11:43
@Caleth Depends how the array is defined. My guess is that this is actually dynamic and OP wants his code to be dynamic too.. — GolezTrol
– GolezTrol, Commented Sep 26, 2017 at 11:46

Caleth · Accepted Answer · 2017-09-26 11:55:41Z

8

You don't need a loop, you are doing one action.

a[std::max(0, std::min(4, (range - 1) / 10))] = value;

edited Sep 26, 2017 at 11:55

answered Sep 26, 2017 at 11:46

Caleth

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5 Comments

GolezTrol Over a year ago

Yeah. It would be (range-1)/10. 30 would lead to 2, 20 would lead to 1. Only range=0 would go wrong, if that would be a possibility. Could optionally be coveredby adding a max as well.

Caleth Over a year ago

@AndyG on balance, neither can I :p

Bathsheba Over a year ago

Methinks you need a floor of 0 in there too.

Quentin Over a year ago

And from C++17, that's a job for std::clamp :)

Neb Over a year ago

Good solution, but, in few weeks, even you will have difficulties understanding what this single line of code does.

Caleth · Accepted Answer · 2017-09-26 12:04:33Z

0

My other answer is very particular to the boundaries being multiples of 10. A runtime modifiable version would be something like

std::set<int> boundaries = { 10, 20, 30, 40, max_range };

// ... potentially modify `a` and `boundaries`, keeping the number of elements equal

a[std::distance(boundaries.begin(), boundaries.lower_bound(range))] = value

answered Sep 26, 2017 at 12:04

Caleth

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Comments

user3608271 · Accepted Answer · 2017-09-26 12:10:17Z

0

I would like it to remove the nested else if's and use a for loop Probably incorrect expression: There's no nested if-else in your example.

Loops, if-else and switch work differently however they all handle conditions:

Loops do iteration; Checking for some condition n times whereas if, switch they check once. So you cannot convert a if-else into a loop.

It's really a good programming trying to make the code effective and as smaller as possible but it is not always the case. If so why such experts build a huge programs with maybe millions of code lines.
Your code works fine.

answered Sep 26, 2017 at 12:10

user3608271

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