Error: conversion from ‘double’ to ‘float’ may change value

Question

5.00/5 (1 vote)

See more:

This consists of two Visual Studio Code files, in C. 

This one, called qdriver.c

<pre>#include <stdio.h>  // printf

void temperature_convertor(float fahrenheit);

int main(void)
{
	// test case 1
	temperature_convertor(0);
	printf("\n");

	// test case 2
	temperature_convertor(20);
	printf("\n");

	// test case 3
	temperature_convertor(300);
	printf("\n");

	// test case 4
	temperature_convertor(-20);
	printf("\n");

	// test case 5
	temperature_convertor(137);
	printf("\n");

	// test case 6
	temperature_convertor(-300);
	printf("\n");

	return 0;
}

linked to this one, called q.c

#include <stdio.h>  
float fahrenheit;
void temperature_convertor(float fahrenheit)
{
	float C = fahrenheit - 32;
    float Ce = C * 5;
    float celsius =  Ce/9;
    float kelvin =  celsius + 273.15;
    printf("fahrenheit celsius  kelvin \n%f %f %f", fahrenheit, celsius, kelvin);
}

When I try running this, it comes out the error

conversion from ‘double’ to ‘float’ may change value

for the line

float kelvin =  celsius + 273.15;

. How do i fix this?

What I have tried:

I'm kind of lost, since I'm quite new to coding

Posted 25-Sep-21 3:45am

Member 15370412

Updated 25-Sep-21 4:52am

Add a Solution

2 solutions

Solution 2

A simple alternative is using doubles instead of floats every where in your program. Don't use floats unless you have scarce resources available (e.g. cross-compiling for a microcontroller).

Posted 25-Sep-21 4:52am

CPallini

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Accepted Answer · 2021-09-25T03:56:00

273.15 is a double value - so when you add it to a float value you get a double value (it always ends up with the "highest precision" type, so the float variable celcius is promoted to a double before the addition).
So when you try to store the result, you are storing a double value in a float variable, and the system is warning you that this could result in the loss of data.

The simplest fix is to use a float constant value instead by adding a "F" suffix:

C

float kelvin =  celsius + 273.15f;