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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.

Practice 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.

Starter code

main.c
#include <stdio.h>

int main(void) {
    double a = 4.5;
    double b = 5.5;
    // average = (a + b) / 2 and print with printf
    return 0;
}

Sample solution

main.c
#include <stdio.h>

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

Expected output

5.000000

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which is a floating-point type?

  • int
  • char
  • double Correct answer
  • void

Explanation: double is a type for decimals.

2 double specifier

Question 
printf("Result: ____", 3.14);
Answer 
printf("Result: %lf", 3.14);

Explanation: %lf is used to print double values.

3 Match the specifiers

Term Meaning
%f Float
%lf Double
%e Scientific
%d Integer

All lessons in Beginner

1 C basics

  1. What is C?
  2. Your first program
  3. Compile and run
  4. Comments
  5. printf and escapes
  6. Summary - C basics

2 Variables

  1. Declaring variables
  2. Variable assignment
  3. const
  4. Variable scope
  5. typedef
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. char
  4. sizeof
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Menu loop
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 I/O

  1. printf formatting
  2. scanf
  3. Multiple inputs
  4. getchar and putchar
  5. puts and fputs
  6. Summary - I/O

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. break and continue
  5. Nested loops
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Array size
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 Strings

  1. String basics
  2. String literals
  3. strlen
  4. strcpy and strcat
  5. strcmp
  6. Summary - Strings

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function prototypes
  5. Recursion
  6. Summary - Functions

13 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. NULL
  5. Pointer arithmetic
  6. Summary - Pointer basics

14 Arrays and pointers

  1. Array name as pointer
  2. Pointer to array
  3. Passing arrays to functions
  4. Pointer loop
  5. Multidim array pointer
  6. Summary - Arrays and pointers

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String functions

  1. strchr
  2. strstr
  3. strtok
  4. sprintf
  5. sscanf
  6. Summary - String functions

17 Structs

  1. Defining structs
  2. Using structs
  3. typedef struct
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Memory and stack

  1. Stack and heap
  2. Automatic storage
  3. malloc
  4. free
  5. calloc and realloc
  6. Summary - Memory and stack

19 Preprocessor

  1. #define
  2. #include
  3. Conditional compilation
  4. Macro functions
  5. Header files
  6. Summary - Preprocessor

20 Beginner final

  1. Project design
  2. Data model
  3. Functions
  4. Memory management
  5. Putting it together