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[Adult Learning Log] C Language - Week 2 Review

[C Language Week 2] Comments, Preprocessor, Variables, and More ○ Key Takeaways from Week 2 Hands-on practice: Simple calculator, monthly salary calculator Learned that most C programs define functions inside the main function Learned three ways to write comments in C Understood what a preprocessor is, why it’s used, and the meaning of directives like #include Learned the structure of functions and the significance of return values Covered variable declarations, identifier naming rules, and standard data types Practiced using printf(), scanf(), and scanf_s() functions ○ Typical Program Structure Most programs follow this pattern: Input → Process → Output ○ Comments in C C supports the following types of comments: Single-line comment: /* This is a single-line comment / Multi-line comment: / This is a multi-line comment */ Since C99: // Comment from here to end of the line ○ Preprocessor Preprocessing refers to tasks performed before compilation starts. Example: #include #include: directive to include external files stdio.h: standard input/output header file stdio = Standard Input Output .h = Header file This allows access to functions like scanf() and printf(). Why use header files? Organize frequently used code (functions, constants, structures, etc.) Reduce duplication, improve modularity and maintenance Directives like #include allow reusable code blocks Example 2: #define _CRT_SECURE_NO_WARNINGS // Used in Visual Studio to suppress scanf warnings ○ Structure of a Function Example: int main(void) { return 0; } int: return type (integer) main: function name (entry point) void: no input parameters { }: function body return 0;: signals successful termination return 0 = Success return 1 or other values = Error or abnormal termination ○ Variables Declaration: int x; // Declares integer variable x float radius; // Declares float variable Standard Data Types: Integer types: short, int, long long Floating-point types: float, double, long double Character type: char (read as “character”) Identifier Rules: Must consist of letters, digits, and underscores (_) Cannot contain spaces First character must be a letter or _ (not a digit) Case-sensitive Cannot use reserved keywords (e.g., int, float) Good names describe purpose: year, bank_account, BankAccount Poor names: i, j, k (unclear meaning) Initialization: int x = 10; int y = 20; int sum = 0; Multiple variables of the same type can be initialized in one line: int width = 100, height = 200; // Recommended int width, height = 200; // Not recommended (only height is initialized) ○ printf() and scanf() printf() Example: int x = 10; printf("%d", x); // %d = decimal integer %d tells printf to print an integer in decimal format scanf() Example: float radius; printf("Enter radius: "); scanf("%f", &radius); & (ampersand) passes the address of the variable so scanf() knows where to store the input ○ Omitting &radius (e.g., scanf("%f", radius);) will cause an error. Use %lf to read a double value (lf = long float) ○ scanf() vs scanf_s() and Security In Visual Studio, using scanf() often triggers a warning recommending scanf_s(). Why? To prevent buffer overflow, which is a common vulnerability. scanf() without input size limits can cause excessive input to overwrite memory This can allow attackers to execute arbitrary code (a classic exploit) This technique is known as pwnable hacking Many systems (Windows, Adobe, UNIX tools) have been exploited in the past due to such vulnerabilities scanf_s() is a Microsoft-specific secure function that forces the developer to specify buffer sizes Not portable to Linux/GCC environments → safer alternatives like fgets() are often used To disable the warning in Visual Studio: #define _CRT_SECURE_NO_WARNINGS ○ Practice Exercises Input two numbers and print the sum Calculate monthly salary based on annual salary

Jun 26, 2025 - 05:00

[Adult Learning Log] C Language - Week 2 Review

[C Language Week 2] Comments, Preprocessor, Variables, and More

○ Key Takeaways from Week 2

Hands-on practice: Simple calculator, monthly salary calculator
Learned that most C programs define functions inside the main function
Learned three ways to write comments in C
Understood what a preprocessor is, why it’s used, and the meaning of directives like #include
Learned the structure of functions and the significance of return values
Covered variable declarations, identifier naming rules, and standard data types
Practiced using printf(), scanf(), and scanf_s() functions

○ Typical Program Structure

Most programs follow this pattern: Input → Process → Output

○ Comments in C

C supports the following types of comments:

Single-line comment:

  /* This is a single-line comment */

Multi-line comment:

  /* This is a
     multi-line
     comment */

Since C99:

  // Comment from here to end of the line

○ Preprocessor

Preprocessing refers to tasks performed before compilation starts.

Example:

#include

#include: directive to include external files
stdio.h: standard input/output header file
- stdio = Standard Input Output
- .h = Header file

This allows access to functions like scanf() and printf().

Why use header files?

Organize frequently used code (functions, constants, structures, etc.)
Reduce duplication, improve modularity and maintenance
Directives like #include allow reusable code blocks

Example 2:

#define _CRT_SECURE_NO_WARNINGS  // Used in Visual Studio to suppress scanf warnings

○ Structure of a Function

Example:

int main(void) {
    return 0;
}

int: return type (integer)
main: function name (entry point)
void: no input parameters
{ }: function body
return 0;: signals successful termination

return 0 = Success

return 1 or other values = Error or abnormal termination

○ Variables

Declaration:

int x;        // Declares integer variable x
float radius; // Declares float variable

Standard Data Types:

Integer types: short, int, long long
Floating-point types: float, double, long double
Character type: char (read as “character”)

Identifier Rules:

Must consist of letters, digits, and underscores (_)
Cannot contain spaces
First character must be a letter or _ (not a digit)
Case-sensitive
Cannot use reserved keywords (e.g., int, float)

Good names describe purpose: year, bank_account, BankAccount

Poor names: i, j, k (unclear meaning)

Initialization:

int x = 10;
int y = 20;
int sum = 0;

Multiple variables of the same type can be initialized in one line:

int width = 100, height = 200;  // Recommended
int width, height = 200;        // Not recommended (only height is initialized)

○ `printf()` and `scanf()`

`printf()` Example:

int x = 10;
printf("%d", x);  // %d = decimal integer

%d tells printf to print an integer in decimal format

`scanf()` Example:

float radius;
printf("Enter radius: ");
scanf("%f", &radius);

& (ampersand) passes the address of the variable so scanf() knows where to store the input

○ Omitting &radius (e.g., scanf("%f", radius);) will cause an error.

Use %lf to read a double value (lf = long float)

○ `scanf()` vs `scanf_s()` and Security

In Visual Studio, using scanf() often triggers a warning recommending scanf_s().

Why?

To prevent buffer overflow, which is a common vulnerability.

scanf() without input size limits can cause excessive input to overwrite memory
This can allow attackers to execute arbitrary code (a classic exploit)

This technique is known as pwnable hacking

Many systems (Windows, Adobe, UNIX tools) have been exploited in the past due to such vulnerabilities
scanf_s() is a Microsoft-specific secure function that forces the developer to specify buffer sizes
Not portable to Linux/GCC environments → safer alternatives like fgets() are often used

To disable the warning in Visual Studio:

#define _CRT_SECURE_NO_WARNINGS

○ Practice Exercises

Input two numbers and print the sum

Calculate monthly salary based on annual salary