Unit 1: Fundamentals of C Programming and Control Structures

1. Fundamentals of C Programming

This section covers the basic building blocks of the C language.

Data Types

Data types define the type and size of data a variable can store.

These can be modified with qualifiers like short, long, signed, and unsigned.

Expressions and Operations

An expression is a combination of variables, constants, and operators that evaluates to a single value.

• Arithmetic Operations: + (add), - (subtract), * (multiply), / (divide), % (modulus/remainder).
• Relational Operations: == (equal to), != (not equal to), >, <, >=, <=. These evaluate to 1 (true) or 0 (false).
• Logical Operations: && (logical AND), || (logical OR), ! (logical NOT).
• Assignment Operation: = (assigns the value on the right to the variable on the left).

Input and Output

C uses standard library functions for I/O. You must #include .

• Output: printf() is used to print formatted output to the console.

  printf("Hello, World!\n");
  printf("The number is: %d\n", myVariable);

• Input: scanf() is used to read formatted input from the console.

  int age;
  printf("Enter your age: ");
  scanf("%d", &age); // & is the "address-of" operator

2. Writing Simple C Programs

A simple C program has a standard structure:

// 1. Preprocessor Directives
#include 

// 2. Main function (execution starts here)
int main() {
    // 3. Variable Declaration
    int a, b, sum;

    // 4. Program Logic / Statements
    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);

    sum = a + b;

    printf("The sum is: %d\n", sum);

    // 5. Return Statement
    return 0; // 0 indicates successful execution
}

3. Control Structures

Control structures allow you to control the flow of your program's execution.

Decision Making (if, switch)

• if Statement: Executes code if a condition is true.

  if (age >= 18) {
      printf("You can vote.");
  }

• if-else Statement: Executes one block if true, another if false.

  if (num % 2 == 0) {
      printf("Even");
  } else {
      printf("Odd");
  }

• else if Ladder: Used for multiple exclusive conditions.

  if (marks >= 90) {
      printf("Grade A");
  } else if (marks >= 80) {
      printf("Grade B");
  } else {
      printf("Grade C");
  }

• switch Statement: Efficiently checks a variable against a list of constant values.

  switch (day) {
      case 1:
          printf("Monday");
          break; // A break is crucial!
      case 2:
          printf("Tuesday");
          break;
      default:
          printf("Invalid day");
  }

Loops (while, do-while, for)

• while Loop: An entry-controlled loop. The condition is checked *before* the loop body executes.

  int i = 1;
  while (i <= 5) {
      printf("%d ", i);
      i++;
  }
  // Output: 1 2 3 4 5

• do-while Loop: An exit-controlled loop. The loop body *always* executes at least once.

  int i = 1;
  do {
      printf("%d ", i);
      i++;
  } while (i <= 5);
  // Output: 1 2 3 4 5

• for Loop: The most common loop. It combines initialization, condition, and increment in one line.

  for (int i = 1; i <= 5; i++) {
      printf("%d ", i);
  }
  // Output: 1 2 3 4 5

Jump Statements (break, continue, goto)

• break: Immediately terminates the innermost loop (for, while, do-while) or switch statement.
• continue: Skips the rest of the current loop iteration and moves to the next iteration.
• goto: Unconditionally jumps to a labeled statement.

  if (error) {
      goto cleanup;
  }
  // ...
  cleanup:
      printf("Cleaning up resources.");

  Exam Tip: Use goto sparingly. It can make code very difficult to read and debug. It's generally considered bad practice but is mentioned in the syllabus.

Nested Loops

A loop inside another loop. This is commonly used for working with 2D arrays or printing patterns.

// Prints a 3x3 square of stars
for (int i = 0; i < 3; i++) {      // Outer loop (rows)
    for (int j = 0; j < 3; j++) {  // Inner loop (columns)
        printf("* ");
    }
    printf("\n"); // Newline after each row
}

4. Problem Solving Applications

This unit requires applying the above control structures to solve elementary problems, such as:

• Mathematics:
  • Finding the factorial of a number (using a for loop).
  • Checking if a number is prime (using a for loop and if).
  • Generating the Fibonacci series (using a while loop).
  • Finding the sum of digits of a number (using a while loop and %).
• Statistics:
  • Calculating the average of n numbers.
  • Finding the maximum and minimum values in a list of numbers.