return value of pow() gets rounded down if assigned to an integer

c pow
ango picture ango · Oct 29, 2011 · Viewed 7.1k times · Source

I am using the pow function in C and storing the return value in an integer type. see the code snippet below:

for (i = 0; i < 5; i++){
    val = (int)pow(5, i);
    printf("%d, ", val);
}

here i, and val are integers and the output is 1, 5, 24, 124, 624. I believe this is because a float 25 is treated as 24.99999... which gets rounded down to 24 on assignment to an integer.

How can I by pass this if I still need to store the return value in an int ?

Answer

Marcelo Cantos picture Marcelo Cantos · Oct 29, 2011

Add 0.5 before casting to int. If your system supports it, you can call the C99 round() function, but I prefer to avoid it for portability reasons.

Related questions

pow function in C

I write a C code that have power function that is from math.h library. when I compiled my program, I received an error which is " undefined reference to 'pow' function ", I compile my program using gcc compiler (fedora 9). I …

Read More
Why is printf not using scientific notation?

I understand that this is a common problem. However I can't find a solid straight answer. 16 ^ 54 = 1.0531229167e+65 (this is the result I want) When I use pow(16,54), I get: 105312291668557186697918027683670432318895095400549111254310977536.0 Code is as follows: #include <stdio.h> #include <…

Read More
Does pow() work for int data type in C?

I was simply writing a program to calculate the power of an integer. But the output was not as expected. It worked for all the integer numbers except for the power of 5. My code is: #include <stdio.h> #…

Read More