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Repetition is the best method for memory; spend one minute each day to remember the basics of C language.

“Essential Knowledge Points for C Language Beginners: Series of 100 Notes“

4. This is the simplest C program universal template, analysis of the basic structure of a C program

1. What does a complete C program look like?

#include <stdio.h>  // Header file inclusion

/* This is a multi-line comment
   used to explain the program's functionality */

int main() {        // Main function entry
    printf("Welcome to learning C language!\n");  // Output statement
    return 0;       // Return value
}

2. Detailed explanation of core components

1. Preprocessor directive (#include)

#include <stdio.h>

• • Function: Introduces the standard input-output library, allowing the program to use<span>printf()</span>, <span>scanf()</span> and other functions
• • Common header files:
• • <span>stdlib.h</span>: Dynamic memory management
• • <span>math.h</span>: Mathematical functions
• • <span>string.h</span>: String handling

2. Comments

// Single line comment
/* Multi-line comment */

• • Function:
• • Explains the functionality of the code (for yourself or others)
• • Temporarily disables code
• • Important principle:
• • Do not write “what this is”, but write “why this is done”

3. main() function

int main() { ... }

• • Program entry: The operating system starts execution from here
• • Return value:
• • <span>return 0</span> indicates success
• • Non-zero values usually indicate error types (e.g., <span>return 1</span>)

4. Function body (code within { })

• • Execution statements: Each statement ends with a semicolon<span>;</span>
• • Code style:

  // Recommended style (indent 4 spaces)
  int main() {
      printf("Hello");
      return 0;
  }
  
  // Not recommended (hard to read)
  int main(){printf("Hello");return 0;}

3. Program execution flow

    A[Start] --> B[Preprocessing]
    B --> C[Compilation]
    C --> D[Linking]
    D --> E[Executing main()]
    E --> F[End]

4. Practical example: Calculate the sum of two numbers

#include <stdio.h>

int main() {
    int a = 5;      // Define variable a
    int b = 3;      // Define variable b
    int sum = a + b; // Calculate sum

    printf("The sum of the two numbers is: %d\n", sum);
    return 0;
}

Output result:

The sum of the two numbers is: 8

5. Common errors

1. 1. Missing semicolon

   printf("Hello")  // Error! Missing;

2. 2. Chinese punctuation

   printf（"Hello"）; // Used Chinese brackets

3. 3. Spelling error in main

   int mian() { ... }  // Error!

6. Code style recommendations

1. 1. Naming: Use English words for variables/functions (e.g., <span>studentAge</span>)
2. 2. Indentation: Use 4 spaces or Tab consistently
3. 3. Bracket style:

   // Style 1 (recommended)
   int main() {
   }
   
   // Style 2
   int main()
   {
   }

7. Summary

• • Must include<span>main()</span> function
• • Statements end with a semicolon
• • Use comments and indentation appropriately

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