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C program for finding remainder from floating point division using fmod

As we have seen in “C program for using modulo operator, finding if number is dividable and print remainder.” if we want to use modulo operator, we have to use either integer or typecast the value with “int” and result also was integer.

Now, what if we have to do float operations and want to identify whether certain float number is completely divisible by another number or not and if not what could be the remainder. For this we have to use math libraries function “fmod” and link the same library during the compilation.

 $ vim remainder_from_float_division.c 
#include <stdio.h>
#include <math.h>       /* fmod */
int main () {
        float i = fmod (15.0,3.0);
        printf("i is %f\n", i);
        if (i==0) {
                printf("number is divisible by 3\n");
        } else {
                printf("number is not divisible by 3\n");
        printf ( "fmod of 5.3 / 2 is %f\n", fmod (5.3,2) );
        printf ( "fmod of 18.5 / 4.2 is %f\n", fmod (18.5,4.2) );
        return 0;

Note: we are passing additional “-lm” to link the math library during compilation.
If you don’t link the same, you may get an error like,

/tmp/ccUbRn5m.o: In function `main':
remainder_from_float_division.c:(.text+0x2c): undefined reference to `fmod'

Above error can be resolved by adding -lm at the end of compilation command.

 $ gcc -o remainder_from_float_division remainder_from_float_division.c -lm 
$ ./remainder_from_float_division
i is 0.000000
number is divisible by 3
fmod of 5.3 / 2 is 1.300000
fmod of 18.5 / 4.2 is 1.700000
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