Unit 1 – Computational Thinking

Computational Thinking (CT) is a problem-solving method used to break down complex tasks into smaller, manageable parts. It involves:

• Decomposition – Breaking problems into smaller units
• Pattern Recognition – Finding similarities in problems
• Abstraction – Removing unnecessary details
• Algorithm Design – Creating step-by-step instructions

Every C program follows a simple but well-defined structure. Understanding these components helps you read, write, and organize code clearly.

        // Basic C Program Structure
        
        // 1. Preprocessor Directives
        #include 
        
        // 2. Global Declarations (optional)
        int globalVar = 10;
        
        // 3. main() Function
        int main() {
        
            // 4. Variable Declarations
            int num = 5;
        
            // 5. Statements
            printf("Number = %d", num);
        
            // 6. Return Statement
            return 0;
        }
            

1. Preprocessor Directives

These lines begin with # and are processed before compilation. The most common directive is #include, which loads header files.

Examples:

• #include <stdio.h> – standard input/output functions
• #include <math.h> – mathematical functions
• #define PI 3.14 – macro definition

2. Global Declarations (Optional)

Variables or functions declared outside main() are global. They can be accessed anywhere within the file.

3. The main() Function

Execution of every C program starts from main(). It can return an integer, usually 0 to indicate success.

4. Variable Declarations

Variables must be declared before use. Declarations specify the data type and name.

        int age;
        float marks;
        char grade;
            

5. Statements & Expressions

Statements perform actions such as assignments, calculations, or printing output. Each statement ends with ;.

6. The Return Statement

return 0; marks successful program completion and returns control to the operating system.

Data types define the type of data a variable can store and how much memory it occupies. C provides several built-in (primitive) types that form the foundation of all operations.

1. Primary (Basic) Data Types

The basic data types in C are:

Type	Description	Typical Size	Format Specifier
int	Stores integer values (positive or negative)	4 bytes	%d
float	Stores single-precision decimal numbers	4 bytes	%f
double	Double-precision decimal values	8 bytes	%lf
char	Stores a single character	1 byte	%c

2. Derived Data Types

These are built from basic types:

• Arrays – Collection of values of the same type
• Pointers – Store memory addresses
• Functions – Block of code returning specific data types

3. User-Defined Data Types

Created by the programmer:

• struct – Group of different data types
• union – Shared memory for multiple variables
• enum – Named integer constants
• typedef – Creates a new name for an existing type

4. Example

        #include 
        
        int main() {
            int age = 20;
            float marks = 85.5;
            char grade = 'A';
            double pi = 3.141592;
        
            printf("Age: %d\n", age);
            printf("Marks: %.2f\n", marks);
            printf("Grade: %c\n", grade);
            printf("PI: %lf\n", pi);
        
            return 0;
        }
            

// Program: Taking user input
#include 

int main() {
    int num;

    printf("Enter a number: ");
    scanf("%d", &num);

    printf("You entered: %d", num);
    return 0;
}
            

Program 1: Add Two Numbers

#include 

int main() {
    int a, b, sum;

    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);

    sum = a + b;

    printf("Sum = %d", sum);
    return 0;
}
            

Program 2: Check Even or Odd

#include 

int main() {
    int n;

    printf("Enter a number: ");
    scanf("%d", &n);

    if(n % 2 == 0)
        printf("Even");
    else
        printf("Odd");

    return 0;
}