C programming comparing floats

Question

Where is the error in my code, super simple yet the comparisons are not outputting the correct values. This function below is in its own file called: FloatingPointRepresentationsFunctions.c

int FloatCompare(float number1,float number2){
    // Write the function to compare and return the corresponding value
    if(number1 < number2){
        return -1;
    }else if(number2 < number1){
        return 1;
    }else{
        return 0;
    }
}

The functions should return -1 if float 2 is greater then float 1, it should return 1 if float 1 is greater then float 2. It then should return 0 if the float values are equal.

My eclipse console output(mingW):

number1: 12.000000 
number2: 11.000000 
Comp: -1
11.000000 is greater than 12.000000

and here is my main c file:

#include <stdio.h>

int main()
{
    float number1 = 0;
    float number2 = 0;

    int comparison;

    number1=12;
    number2=11;
    printf("number1: %f \nnumber2: %f \n", number1, number2);
    comparison=FloatCompare(number1,number2); // Compare two floating point numbers
    printf("Comp: %d\n", comparison);
    if(comparison==1){
            printf("%f is greater than %f\n",number1,number2);
    }else if(comparison==-1){
                printf("%f is greater than %f\n",number2,number1);
    }else if(comparison==0){
        printf("Number are equal\n");
    }else{
        printf("Error\n");
    }


    return 0;
}

Answer 1

Your main file doesn't have a proper prototype for FloatCompare . This means it assumes the default function definition of int FloatCompare() , which results in the function being called incorrectly and undefined behavior .

You need to add a declaration to your main source file so it knows how to call the function properly.

#include <stdio.h>

int FloatCompare(float number1,float number2);

int main()
{
...
}