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Type conversion

Learn implicit and explicit (cast) type conversion.

Type conversion

Type conversion means turning a value into another type. There are two kinds:

  • Implicit: the compiler does it automatically (e.g., int x = 3.7;)
  • Explicit: done with the cast operator ((int)3.7 → 3)

Explicit conversion, also called a cast, is safer because it states your intent clearly and silences warnings.

Conversion rules

Type conversion in C follows clear rules:

  • int to double: safe, no data loss
  • double to int: decimal part is lost
  • Conversion to a smaller type risks overflow

Type matching matters especially in division: 7 / 2 gives 3 (integer division), but 7.0 / 2 gives 3.5 (double division).

Practice Print with cast

Add to the program below a line that casts d to int with (int) d, and a printf call. The output should be 9 9.700000.

Starter code

main.c
#include <stdio.h>

int main(void) {
    double d = 9.7;
    // cast to int and print with printf
    return 0;
}

Sample solution

main.c
#include <stdio.h>

int main(void) {
    double d = 9.7;
    int i = (int) d;
    printf("%d %lf", i, d);
    return 0;
}

Expected output

9 9.700000

Questions and answers

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

1 What does (int)3.7 return?

  • 4
  • 3 Correct answer
  • 3.7
  • 0

Explanation: (int)3.7 drops the decimal part and gives 3.

2 Cast operator

Question 
int x = (____) 3.7;
Answer 
int x = (int) 3.7;

Explanation: (int) converts a value to int.

3 Match conversion concepts

Term Meaning
(int) To int
(double) To double
implicit Automatic
explicit Cast

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