How to take first 5 numbers of float

Question

float number=15.555555;
printf("FIRST FIVE NUMBERS%f",number);

Desired ouput:

FIRST FIVE NUMBERS15555

Actual output:

FIRST FIVE NUMBERS15.555555

How do I get the 5 digit number and discard the decimal point?

For example:

123.43213 -> 12343

1.5634567 -> 15634

What exactly are you asking? The question is not clear. Do you really want to print out 15555? not 15.555? — Trent, Dec 09 '14 at 19:07
Do you want `15555` or `15.555` as output? Please edit your question. — Basile Starynkevitch, Dec 09 '14 at 19:12
@Columbo I believe this is a good question. I have edited it and would like to see it reopened. — Jonathan Mee, Dec 10 '14 at 14:00

score 1 · Accepted Answer · 2014-12-09T21:04:39.833

1

Without elegance, some brute force and rounding, you might do:

#include <cmath>
#include <iostream>

int main()
{
    double number = 15.555555;
    while(100000 <= number) number /= 10;
    while(number < 10000) number *= 10;
    // 10000.x <= number < 100000
    number = round(number);
    if(100000 <= number) number = round(number/10);
    std::cout << number << '\n';
}

Note: Only for numbers greater than zero.

edited Dec 09 '14 at 21:04

answered Dec 09 '14 at 19:29

Well,when it rounds my number,last digit (5) changes into 6 ...So instead of 15555 i get 15556 :/ – user3751721 Dec 09 '14 at 20:20
1

@user3751721 you might use 'trunc' instead – Dec 09 '14 at 20:25
1

@DieterLücking You should probably check that number is greater than 1. This solution gets wrecked pretty hard if it's not. – Jonathan Mee Dec 09 '14 at 20:51
@JonathanMee I don't see that, but a negative (zero) number, indeed! – Dec 09 '14 at 20:55
@DieterLücking Yup, sorry that should have read greater than 0. – Jonathan Mee Dec 09 '14 at 20:58
@DieterLücking Lol, I guess that's one way to fix the answer, I was looking at patching the code using `log` but that goes haywire if you have negatives too. – Jonathan Mee Dec 09 '14 at 21:15
@JonathanMee I avoided that, there might be some clever alternatives. – Dec 09 '14 at 21:26

score 0 · Answer 2 · edited May 23 '17 at 11:50

0

You can always do something like this:

cout << "FIRST FIVE NUMBERS" << to_string(15.555555).substr(0, 5);

That won't round or anything but maybe it's what you want?

EDIT:

Per Lightness Races in Orbit's comment I think the desired result can be obtained from:

string foo = to_string(15.555555);

for_each(foo.begin(), advance(foo.begin(), min(5, foo.size())), [](const char& i){if(i != '.')cout << i});

edited May 23 '17 at 11:50

Community

1
1

answered Dec 09 '14 at 19:40

Jonathan Mee

37,899
23
129
288

Strip the decimal point and you're there. – Lightness Races in Orbit Dec 09 '14 at 19:40
@LightnessRacesinOrbit Is that what he wants? It seems like he just used %f so print the whole thing? Ha, I learned this from your answer this morning! – Jonathan Mee Dec 09 '14 at 19:41
According to both of the examples in the question, yes. – Lightness Races in Orbit Dec 09 '14 at 19:41
Sorry not sure what you mean about this morning – Lightness Races in Orbit Dec 09 '14 at 19:42
@LightnessRacesinOrbit Ah took that to mean an American comma: 1,000,000 – Jonathan Mee Dec 09 '14 at 19:43
@LightnessRacesinOrbit http://stackoverflow.com/a/27380559/2642059 – Jonathan Mee Dec 09 '14 at 19:43
Oh that I see :) Oh my god I haven't moved since then :( – Lightness Races in Orbit Dec 09 '14 at 19:44

How to take first 5 numbers of float

2 Answers2