mod operator on floating point values in c. This is showing error "illegal use of floating point"

Question

#include<stdio.h>
#include<conio.h>
void main()
{
  float n, r;
  printf("\n enter a number");
  scanf("%d",&n);
  r=n%10;
  n/=10;
  printf("%d %d",n, r );
  getch();
}

This code is showing error while compiling. I want to know: can we perform mod operation on floating point values?

Please read the manual for `scanf`, including what the `%d` format specifier does, and what type of arguments are expected when you use it. — Nate Eldredge, Sep 23 '17 at 17:20
*can we perform mode operation on floating point values*: **No**. — haccks, Sep 23 '17 at 17:20
"can we perform mod operation on floating point values?" not quite. C has `fmodf()` which is the same as the Euclidean "mod operation" for positive values. In C `fmodf()` does a "remainder" which differs from "mod" when an operand is negative. — chux - Reinstate Monica, Sep 23 '17 at 20:13

James Maa · Answer 1 · 2017-09-23T20:25:30.137

5

No, you can't use % on float

Use fmod function instead Referenced here: http://www.cplusplus.com/reference/cmath/fmod/

Or fmodf http://en.cppreference.com/w/c/numeric/math/fmod

r = fmod (n, 10)

You need to #include <math.h> to use this function

Also, you should do scanf(%f, &n) to read in the float

#include<stdio.h>
#include<math.h>

int main()
{
  float n, r;
  printf("\n enter a number");
  scanf("%f", &n);
  r=fmod(n,10.0);
  //r = fmodf(n, 10.0); thansk to chux
  n /= 10;
  printf("%f %f", n, r );
}

edited Sep 23 '17 at 20:25

answered Sep 23 '17 at 17:23

James Maa

1,764
10
20

Can you also mention the error that @NateEldredge alluded to? – Weather Vane Sep 23 '17 at 17:25
@WeatherVane sure – James Maa Sep 23 '17 at 17:30
`fmodf()` makes more sense for `float` arguments. – chux - Reinstate Monica Sep 23 '17 at 20:14
@chux it does, but c would implicitly convert 10 to 10.0 in this case – James Maa Sep 23 '17 at 20:15
True, yet with `fmod()`, the `n` is converted from `float` to`double`. Then `fmod()` computes the `double` remainder and then `r = ` converts that `double` remainder to `float`. `fmodf()` is likely faster than `fmod()` and code avoids the 2 conversions of `float` to `double` and `double` to `float`. – chux - Reinstate Monica Sep 23 '17 at 20:22
@chux it is a great point, I would keep this in mind in my future – James Maa Sep 23 '17 at 20:23
Most `` functions have `float` and `long double` versions. – chux - Reinstate Monica Sep 23 '17 at 20:26
@chux, seems in `c++98` and the following versions, these function has actually been combined, into `fmod()` with multiple overloaded versions? – James Maa Sep 23 '17 at 20:28
This question/answer is `C`, my comments reflect that. Other languages like `c++98`, as well as Java, C# and a new [JM-C](https://stackoverflow.com/users/8157511/james-maa) may do other things. – chux - Reinstate Monica Sep 23 '17 at 20:32

mod operator on floating point values in c. This is showing error "illegal use of floating point"

1 Answers1