Why a long double variable shows minus zero?

Question

When I initialize a long double variable with '1' in the following program, I get the output as -0.000000. Why it showing minus sign before zero? because that's mathematically not correct.

#include <stdio.h>

int main()
{
    long double a;
    
    a = 1;
    
    printf("%Lf", a);

    return 0;
}

Output:

-0.000000

Answer 1

Hi Debojit Acharjee,

Normally this doesn't happen, please tell me what compiler you are using? What is an operating system? Here's what I get in VS2022:

Assigns the integer constant 1 to the long double variable a and prints it using the %Lf format string. According to the C language standard, the integer constant 1 is implicitly converted to type long double in this case. Regarding the issue with the output being -0.000000 , this may be due to the default printing precision for long double types.

You can specify a higher printing precision. I suggest you use %.0Lf to print an integer value and make sure no fractional part is displayed.

printf("%.0Lf", a);

If you want the decimal part to appear in the output, I suggest you use the %.6Lf format string, where .6 means set the printing precision to 6 decimal places.

You could also try printf("%Le", a); to output it using scientific notation.

Best regards,

Elya Yao

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Answer 2

you must have a compiler issue

on a mac with xcode, I get 1.000000

with the online c compiler : https://www.onlinegdb.com/online_c_compiler

I get the proper 1.000000