CODEWITHSUNDEEP
cfloating-pointtypecast-operator
Darwin57721
Darwin57721

Reputation: 197

Unknown behaviour while typecasting a float to an int.

I wanted to typecast a float with the following code. change is a float and changeI is an int. The tricky input value is 0.41 since it can't be accurately represented in binary but I don't understand why this does not work.

changeI = (int)(change*100)

If I print just (change*100.0) it prints 41.0000003 or something equivalent, which to my understanding if I typecast i.e (int) it should just drop the floating point bits and leave the number as 41.

However, if I print the value of changeI I get 413 and I don't really know why.

Also, if I manually print (int)41.0000003 it is also printed as 413

Edit:

Ok, so I found the main problem, which is really stupid by the way (i was printing an extra 3 afterwards and forgot the new line character in the previous print but now it prints 40 instead of 41). This is the full code. 

int flag = 0;
float change;
int changeI;

do{
    printf("How much change is owed?: ");
    scanf("%f", &change);
    if (change >= 0){
         flag = 1;
    }
}while(!flag)

changeI = (int)(change*100.0);

printf("%f\n", change*100.0);
printf("%i\n", changeI);
printf("%i\n", (int)(41.0000003));

The output for 0.41 is:

>41.0000003
>40
>41

Edit2: As JackV stated, if you copy the float multiplied by 100 to another float and then typecast that new float it does print 41 but I would still like to know why does this happens.

Upvotes: 0

Views: 81

Answers (1)

JackV
JackV

Reputation: 218

I dont know exactly what you are doing but this:

#include<stdio.h>

int main()
{
    int changeI, newI;
    float change = 0.41, var = change * 100;
    changeI = (int)(change*100);
    newI = (int)(var);
    printf("%f", var); //prints 41.000000
    printf("int = %d\n", changeI); //prints 40
    printf("float = %f", change); //prints 0.410000
    printf("%d", newI); //prints 41
    return 0;
}

Works exactly as it should it prints:

int = 40

float = 0.410000

Upvotes: 1

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