How to know if a number is positive or negative or 0

Question

Is it possible to know if a number is positive or negative or 0 in c language using only two if conditions?

If yes, then how? please let me know

Yes I am, I tried with terinary operator, switch case also, but every where it is taking 3 conditions — user2753523, Feb 26 '14 at 07:39
You need 2 comparisons. 1: Negative or not. 2: (if not negative, 0 or negative) — Toon Krijthe, Feb 26 '14 at 07:40
@Lundin I was prompted to mark it a duplicate after looking at an answer that seemed like a _verbatim copy-paste_ from my answer to the linked question. — devnull, Feb 26 '14 at 07:43
This question appears to be off-topic because only escapees from the lunatic asylum would ever do such a thing. SO is supposed to be about real problems that you face, not arbitrarily limited things that no-one would ever encounter :-) — paxdiablo, Feb 26 '14 at 07:46
@user2753523 if you have tried something show us that, if you ask question like you will get down votes so better edit your question and show us what you have tried. — Omer Obaid, Feb 26 '14 at 07:48
In any case, the following fits your description: `if (x < 0) {puts ("-ve");} else {if (x > 0) {puts ("+ve");} else {puts ("zero");}} — paxdiablo, Feb 26 '14 at 07:48

score 3 · Answer 1 · edited Feb 26 '14 at 07:53

3

Use only two ifs:

if (num <= 0) {
      if (num == 0) {
          /* num is zero */
      } else {
          /* num is negative */
      }
} else {
    /* num is positive */
}

edited Feb 26 '14 at 07:53

Sangeeth Saravanaraj

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answered Feb 26 '14 at 07:47

Lee Duhem

14,695
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3

Mmm.. if `num` is zero, your code would first say that it's zero, then say it's negative, and then positive. Isn't it? – devnull Feb 26 '14 at 07:49
are you sure you r not missing else? – Omer Obaid Feb 26 '14 at 07:49
@devnull You are right, `else`s are missed. – Lee Duhem Feb 26 '14 at 07:58

Omer Obaid · Answer 2 · 2014-02-26T07:59:45.320

I hope this can solve your problem

#include <stdio.h>
int main()
{
    float num;
    printf("Enter a number: ");
    scanf("%f",&num);    // Take input from user
    if (num<=0)          // if Number is >= 0
    {                    
        if (num==0)      // if number is equal to zero
          printf("You entered zero.");
        else             // if number is > 0
          printf("%.2f is negative.",num);
    }
    else                // if number is < 0
      printf("%.2f is positive.",num);
    return 0;
}

chux - Reinstate Monica · Answer 3 · 2014-02-26T08:34:08.057

If c is a floating point, the problem becomes interesting.

c may be
1) > 0
2) < 0
3) = 0
4) "Not-a-Number"

#include <math.h>
...
int classification = fpclassify(x); 
if (classification == FP_NAN || classification == FP_ZERO)) {
  if (classification == FP_NAN) puts("NaN")
  else puts("zero");
}
else  {
  if (signbit(x)) puts("< 0" )
  else puts("> 0");
}

At most, 2 if()s executed.

Without using classification functions/macros

if (x != x || x == 0.0)) {
  if (x != x) puts("NaN")
  else puts("zero");
}
else  {
  if (x < 0.0) puts("< 0" )
  else puts("> 0");
}

How to know if a number is positive or negative or 0

3 Answers3