MMGameslogo  MMGames  Introduction to
C Language  C Language
Development  C language
in the browser  Handy App
TwitterSharebutton  FacebookSharebutton  はてブbutton  RSSbutton  Japanese Version 
MMGameslogo  MMGames
TwitterSharebutton  FacebookSharebutton   

Introduction to
C Language

C language
in the browser

Handy App
Read it right next to your computer.
Book version bitter C
Read it right next to your computer.
Book version bitter C
Read it right next to your computer.
Book version bitter C
Read it right next to your computer.
Book version bitter C
learn through sufferingC Language
learn through sufferingC Language

Handling Immutable Values

Constant value throughout
Values that do not change during execution are called constants.
So far, any numbers written directly into the program have been constants.
Strings directly written are also constants and are called string literals.

In programming, you often use the same numbers or strings repeatedly.
For example, pi is approximately 3.14159, and this value remains constant at all times.

Like this, writing the same value or string repeatedly is wasteful.
Also, if it becomes necessary to change those numbers or strings, it's a hassle to correct them.

For example, if there were a calculator software with a function to calculate consumption tax,
"What if the consumption tax suddenly increased from 3% to 5%?"
現在ではそれどころではなくなってしまいましたが・・・
We need to replace all instances of the number 0.03 in the program with 0.05.
There might be a 0.03 with a meaning other than consumption tax.
It's quite a laborious process to rewrite it, checking each one individually to avoid making mistakes.

Therefore, we will assign names to the numerical values and use those names.
Just modify the named section, and all the numbers will be corrected.
If it's labeled with a name, it's easier to understand than just a number.
Naming numbers
C has a mechanism for naming numeric values.
That is a #define pseudo-instruction.
The usage of #define pseudo-instructions is as follows.

#define pseudo-instruction 
#define 名前 numerics

First, with the #define preprocessor directive, do not put a semicolon at the end of the line.
Also, it's common to place this statement at the beginning of the program.
Also, while the same characters can be used in names as in variables, uppercase letters are generally used.
The following program takes a base price as input and displays the price including tax.

#define pseudo-instruction 
#include <stdio.h>

#define EXCISETAX 0.03 /* ここでConstantを宣言 */

int main(void)
{
    int price;

    printf("本体価格:");
    scanf("%d", &price);
    price = (int)((1 + EXCISETAX) * price); /* Constant使用 */
    printf("税込価格:%d\n", price);

    return 0;
}

"If you run this program and enter 300 as input, the result will be as follows:"

Execution results
本体価格:300 (入力値)
税込価格:309

This program uses constants defined by `#define` pseudo-instructions for numerical calculations.
"I'm using the name EXCISETAX in the formula for calculating the inclusive price,"
This name is replaced with 0.03 by the leading #define pseudo-instruction.

"Since the number 0.03 replacing EXCISETAX in this formula is a real number,"
"The calculation results are also real numbers, but normally real numbers aren't used for prices."
Casting to an integer and assigning it.

Changing the value in a #define statement will change the corresponding numerical values in the program.
The following is a snippet of code that changes the sales tax to 0.05.

Change the consumption tax to 0.05. 
#define EXCISETAX 0.05 /* ここでConstantを宣言 */

"If you run this program and enter 300 as input, the result will be as follows:"

Execution results
本体価格:300 (入力値)
税込価格:315

In this way, using constants makes the meaning of numbers clearer and makes corrections easier.
Name the string.
The #define pseudo-instruction allows you to name not only numbers, but also strings.
The usage is the same as with numbers, but for strings, you'll of course need to enclose them in "".
The following program displays the author's name.

Source code 
#include <stdio.h>

#define AUTHOR "Masanori Moriguchi"

int main(void)
{
    printf("作者名:%s\n", AUTHOR);
    return 0;
}

The results of this program's execution are as follows:

Execution results
Author: Masanori Moriguchi

Here, AUTHOR will also be replaced with "Masanori Moriguchi."
"Of course, modifying the #define pseudo-instruction will affect all AUTHORS."


About This Site

Learning C language through suffering (Kushi C) is
This is the definitive introduction to the C language.
It systematically explains the basic functions of the C language.
The quality is equal to or higher than commercially available books.

Part 0: Program Overview
  1. What is a program?
Chapter 1: The World's Smallest Program
  1. A do-nothing program.
  2. A compiler is a translation software.
  3. Practice Problem 1
Chapter 2: How to Write Programs
  1. Rules of Writing
  2. Conventions of writing
  3. Practice Problem 2
Chapter 3: Displaying on the Screen
  1. String Display
  2. newline character
  3. Practice Problem 3
Chapter 4: Displaying and Calculating Numbers
  1. Display of numbers
  2. Basic calculations
  3. Numeric types
  4. Practice Problem 4
Chapter 5: Numerical Memory and Calculation
  1. Memorizing numbers.
  2. Types of Variables
  3. Type conversion
  4. Number formatting
  5. Practice Problem 5
Chapter 6: Input from the Keyboard
  1. input function
  2. The fear of input
  3. Practice Problem 6
Chapter 7: Comparison and Judgment
  1. Comparative sentences
  2. Comparison operators
  3. Execution of multiple processes
  4. Problem 7
Chapter 8: Performing Case-by-Case Processing
  1. Two cases
  2. Cases with three or more possibilities.
  3. Case by case basis
  4. Practice Problem 8
Chapter 9: Repeating a Fixed Number of Times
  1. Iterative sentence
  2. How Loops Work
  3. Practice Problem 9
Chapter 10: Repeating Without Knowing the Number of Times
  1. Unspecified loop
  2. Input validation
  3. Practice Problem 10
Chapter 11: How to Create Functions
  1. Creating custom functions
  2. Passing a number to a function.
  3. Return a number from a function.
  4. Practice Problem 11
Chapter 12: Variable Lifetime
  1. Variables with limited scope
  2. The last variable standing
  3. Variables that survive within a function
  4. Practice Problem 12
Chapter 13: Handling Multiple Variables at Once
  1. Handling multiple variables collectively.
  2. Arrays
  3. Practice Problem 13
Chapter 14: How to handle strings
  1. Handling Characters
  2. Ways to handle strings
  3. String manipulation functions
  4. Practice Problem 14
Chapter 15: How Pointer Variables Work
  1. The Mechanism of Memory
  2. Variables and Memory
  3. &付けが必要なvariableの正体
  4. Variable to store an address
  5. Let's try using pointer variables.
  6. Passing information through arguments
  7. &The Peculiar Relationship Between Arrays and Pointers
  8. Practice Problem 15
Chapter 16: Combining Multiple Types
  1. Combining variables of different types.
  2. Structure arguments
  3. Array of Structures
  4. Practice Problem 16
Chapter 17: Handling Files
  1. Reading and writing text files
  2. Reading and writing binary files
  3. Drug response
  4. Practice Problem 17
Chapter 18: Macro Functions
  1. Handling Immutable Values
  2. Constants by other means
  3. Implementing simple functions.
  4. Practice Problem 18
Chapter 19: Dynamic Arrays
  1. Create arrays freely.
  2. Practice Problem 19
Chapter 20: Multiple Source Files
  1. Minimal partitioning
  2. The Divide Principle
  3. Practice Problem 20