Why is scanf not accepting my input?

Question

0.00/5 (No votes)

See more:

No matter what input I give this code, the format is messed up and the values do not match what they are supposed to:

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <float.h>
#include <string.h>

double input1 = 0;
int main()
{
    double  celsius1, kelvin1, rankine1;
    scanf ("%g", &input1);
    celsius1 = ((5 *(input1 - 32))/9);
    rankine1 = (input1 + 459.67);
    kelvin1 = ((5*rankine1)/9);
    printf("%g degrees Fahrenheit\n%g degrees Celsius\n%g degrees Kelvin\n%g degrees Rankine", input1, celsius1, kelvin1, rankine1);
    return 0;
}

Here is the output for an input of -460.67

-460.67
1.62382e-314 degrees Fahrenheit
-17.7778 degrees Celsius
255.372 degrees Kelvin
459.67 degrees Rankine
C:\Users\rthom\source\repos\ConsoleApplication1\Debug\ConsoleApplication1.exe (process 20956) exited with code 0.

I am required to use %g on this assignment for all variables as well, so there is no way I'd be able to change that.

What I have tried:

I've tried initializing input1 outside and inside of main. I've also tried declaring the variable in main, but regardless of what I've done it hasn't worked. When I've initialized input1 inside main and removed the &, I receive a null pointer != result exception.

Posted 14-Jul-20 14:04pm

Ryan Thomsen

Updated 14-Jul-20 14:39pm

v2

Add a Solution

1 solution

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)

Jon McKee · Accepted Answer · 2020-07-14T14:39:00

Solution 1

scanf - C++ Reference[^]

Specifier chart is near the bottom. It's because '%g' only handles floats (4 bytes) not doubles (8 bytes). You'd need to use '%lg' for doubles. Changing the variables to float worked for me.

Posted 14-Jul-20 14:39pm

Jon McKee

Comments

Ryan Thomsen 14-Jul-20 21:12pm

Unfortunately my assignment specifies I must use type double for all variables and that I must use printers %g conversion specifier to display all numeric values. Is there a workaround to this?

Jon McKee 15-Jul-20 0:46am

I hope you figured it out. If the instructions actually require you to read doubles as if they were floats like this I would ask the teacher about it.

This code will show you what I'm talking about if you enter the same value twice. Floats and doubles have different memory formats.

int main()
{
	double input1 = 0;
	
	//Different precision reads
	scanf("%g", &input1);
	printf("G (float) read: %g\n", input1);
	scanf("%lg", &input1);
	printf("LG (double) read: %g\n", input1);

	//Examining the hex of double vs float
	printf("\nRaw double: %-g\t\t0x", input1);
	for (int i = 0; i < sizeof(double); i++)
		printf("%02X", *(((unsigned char *)&input1) + i));
	printf("\n");
	float input2 = (float)input1;
	printf("Casted float: %-g\t\t0x", input2);
	for (int i = 0; i < sizeof(float); i++)
		printf("%02X", *(((unsigned char *)&input2) + i));
	printf("\n");
	return 0;
}

You can technically pull this off but it's super hacky, may not work on all systems, and never recommended:

scanf("%g", &input1);
printf("%g\n", *((float *)&input1));