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C Brain Teasers: Exercise Your Mind

Discussion: Count the Digits

Explore the intricacies of printf formatting for floating point numbers in C, focusing on width, precision, and rounding. Understand how to use the M_PI constant and how to interpret printf's return value to count output characters accurately.

We'll cover the following...

Run the code

Now, it's time to execute the code and observe the output.

C
#include <stdio.h>
#include <math.h>
int main()
{
    printf("%2.4f\n", M_PI); /* M_PI = 3.14159265358979323846 */
    return(0);
}

Understanding the output

The defined constant M_PI is declared in the math.h header file. It represents the value of π out to 20 digits. Any floating point value could be specified in the printf() statement, though M_PI represents a known value with oodles of digits after the decimal.

The %2.4f placeholder directs the printf() statement to output a floating point value in a width of six digits: a minimum of two to the left of the decimal and four to the right. Because only one digit is to the left of the decimal, one character is output; a space isn’t added. For the right of the decimal, only four digits are ...