C - printf with pow function issue

Question

I am trying to learn some C and I have an issue I can't figure out. Seems pretty simple but the below is not working.

#include <stdio.h>
#include <stdlib.h>

int main() {

    printf("%f", pow(4, 3) );
    return 0;
}

Error:

Implicitly declaring library function 'pow' with type 'double (double, double)'

I have the string formatter set to float so I am not sure why I am seeing that error

What header contains the function prototype for the pow function? — nicomp, Mar 19 '21 at 17:01
That's not an error, it's a warning. You can still run the executable — Dock, Mar 19 '21 at 17:02
@EugeneSh. Thank you. The tutorial I am watching does not have that in the code, I dont know how theirs is even running. It matches mine exactly. Adding that fixed it. — JD2775, Mar 19 '21 at 17:04
Be very careful with C tutorials, many of them are really not worth the time. Always have a [high-quality reference book](https://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list) on hand to validate anything you're being taught. — tadman, Mar 19 '21 at 17:04
@Dock, whether it's a warning or error is configurable in most compilers. Many of us would treat that as an error. — jwdonahue, Mar 19 '21 at 17:06
I have a "C - Primer Plus" book I bought years ago but never really looked at. Maybe I would be better off working with that :). Thanks everyone — JD2775, Mar 19 '21 at 17:07
@Dock. Without prototype the compiler will assume `int` type return value and only pass an `int` to `printf` which might not be a syntax error but will still result in garbage. — Gerhardh, Mar 19 '21 at 17:07

score 0 · Answer 1 · edited Mar 19 '21 at 18:55

0

The pow() is in math.h header file.
The format specifier for double should be used.

edited Mar 19 '21 at 18:55

Obsidian

answered Mar 19 '21 at 17:04

Reynadess

What's wrong with the format specifier? `printf` expects a `double` argument for `%f`. – Gerhardh Mar 19 '21 at 17:05
2

I mistakenly commented (deleted) that `%lf` should be used, but that is for `scanf()`. The `%f` with `printf()` is good, and `float` is promoted to `double`. – Weather Vane Mar 19 '21 at 17:06

score 0 · Answer 2 · answered Mar 19 '21 at 17:34

0

include library #include <math.h> and change printf("%f", pow(4, 3) ) line to printf("%lf", pow(4, 3) ) , because pow() returns double

answered Mar 19 '21 at 17:34

Kanony

3

`%f` is fine for `double` in printing. – Eric Postpischil Mar 19 '21 at 17:36
@EricPostpischil +1 – Kanony Mar 19 '21 at 17:38

2 Answers2