Floating-point types

Learn float, double and long double types.

Floating-point types

C has two types for decimals:

float: single precision (usually 4 bytes, ~7 digits)
double: double precision (usually 8 bytes, ~15 digits)

The default choice is double for higher precision. With printf you use %f or %lf. Constants like 3.14 are double by default.

Precision and scientific notation

float uses less memory but has lower precision. double uses more memory but is more precise. Prefer double for sensitive values like money or measurements.

For very large or small numbers you can use scientific notation:

double avogadro = 6.022e23;
printf("%e", avogadro);

The %e specifier prints the number in exponential form.

Exercise Compute the average

Add the line that computes the average and a printf call to the program below. Find the average with avg = (a + b) / 2; and print it with %lf.

Show example solution

#include <stdio.h>

int main(void) {
    double a = 4.5;
    double b = 5.5;
    double avg = (a + b) / 2;
    printf("%lf", avg);
    return 0;
}

Test yourself

Which is a floating-point type?
- int
- char
- double
- void
Show answer

double — double is a type for decimals.

double specifier

printf("Result: ____", 3.14);

Show answer

printf("Result: %lf", 3.14);

Match the specifiers

%f

Float
%lf

Double
%e

Scientific
%d

Integer

Next lesson: char

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