CODEWITHSUNDEEP
c++casting
Brad
Brad

Reputation: 9

Why does type casting from "int" to "float" cut my value in half?

I was testing out type casting in C++ today after reviewing a past quiz and can't for the life of me figure out why my 'x' value changes from 9 to 4.5000 in the following code.

int main(){
    int x = 9, y = 2;
    float z;
    z = (float)x/(float)y;
    printf("\n%f", z);
    printf("\n%f", x);
    printf("\n%d", x);
}

Outputs

4.5000
4.5000
9

I'd appreciate any help!

Upvotes: 0

Views: 154

Answers (3)

Vivek V K
Vivek V K

Reputation: 1148

It is not cutting your X in half. look at the code below it still prints 4.5

#include <stdio.h>

int main(){
    int x = 9, y = 2;
    float z;
    z = (float)x/(float)y;
    x = 15;
    printf("\n%f", z);
    printf("\n%f", x);
    printf("\n%d", x);
}

this prints:

4.500000
4.500000
15

May be it has to do internally with how floats and ints are stored on stack. Its fishy because its the first float value that gets stored. If I change the code to this:

#include <stdio.h>
using namespace std;

int main(){
    int x = 11, y = 2;
    float z;
    z = (float)x/(float)y;
    x = 15;
    printf("\n%f", z);
    printf("\n%f", x);
    printf("\n%d", x);
}

the output is 

5.500000
5.500000
15

If you dont print the variable z, then the output becomes

0.000000
15

So may be it has to do with the order of printing.

Upvotes: 0

Amadan
Amadan

Reputation: 198476

In printf("\n%f", x) with an int x, you are not casting x to float - you're assuming it's a float. It's like handing a firefighter a stick of butter and telling him it's a fire extinguisher - won't work right.

In order to cast, you either have to assign the value to a cast-compatible variable:

float floatX = x;
printf("\n%f", floatX);

or use the cast operator:

printf("\n%f", (float)x);

Upvotes: 6

Jonathan Potter
Jonathan Potter

Reputation: 37192

The printf function is expecting a float to be on the stack (because of %f) and you've only provided an int.

You need to cast x to a float in that case:

printf("\n%f", (float)x);

Upvotes: 8

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