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Control Flow: Conditional Statements (if, else, switch)

Using `if`, `else`, and `switch` statements to control the flow of execution based on conditions.

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Conditional Statements in C

Explanation: Conditional Statements

Conditional statements are fundamental control flow structures in C programming that allow you to execute different blocks of code based on whether a specified condition is true or false. They enable your programs to make decisions and behave dynamically according to various inputs and circumstances. The main conditional statements are if, else, and switch.

  • if statement: Executes a block of code if a specified condition is true.
  • else statement: Executes a block of code if the condition in the preceding if statement is false.
  • else if statement: Allows you to chain multiple conditions together, providing a more complex decision-making structure.
  • switch statement: Selects one of several code blocks to execute based on the value of a single expression. It's particularly useful when dealing with a fixed set of possible values.

Understanding and effectively using conditional statements is crucial for writing robust and adaptable C programs.

Practical Examples and Case Studies

Example 1: Determining if a number is positive, negative, or zero using if and else if

This example demonstrates how to use if and else if statements to classify a given number as positive, negative, or zero. 

 #include <stdio.h>

int main() {
  int number;

  printf("Enter an integer: ");
  scanf("%d", &number);

  if (number > 0) {
    printf("%d is positive.\n", number);
  } else if (number < 0) {
    printf("%d is negative.\n", number);
  } else {
    printf("%d is zero.\n", number);
  }

  return 0;
}

Case Study 1: Simple Grading System using if, else if, and else

This case study implements a simple grading system that assigns letter grades (A, B, C, D, F) based on a student's score. 

 #include <stdio.h>

int main() {
    int score;

    printf("Enter the student's score: ");
    scanf("%d", &score);

    if (score >= 90) {
        printf("Grade: A\n");
    } else if (score >= 80) {
        printf("Grade: B\n");
    } else if (score >= 70) {
        printf("Grade: C\n");
    } else if (score >= 60) {
        printf("Grade: D\n");
    } else {
        printf("Grade: F\n");
    }

    return 0;
}

Example 2: Determining the Day of the Week using switch

This example uses a switch statement to display the corresponding day of the week based on a numerical input (1-7). 

 #include <stdio.h>

int main() {
    int day;

    printf("Enter a number (1-7) representing the day of the week: ");
    scanf("%d", &day);

    switch (day) {
        case 1:
            printf("Sunday\n");
            break;
        case 2:
            printf("Monday\n");
            break;
        case 3:
            printf("Tuesday\n");
            break;
        case 4:
            printf("Wednesday\n");
            break;
        case 5:
            printf("Thursday\n");
            break;
        case 6:
            printf("Friday\n");
            break;
        case 7:
            printf("Saturday\n");
            break;
        default:
            printf("Invalid input. Please enter a number between 1 and 7.\n");
    }

    return 0;
}

Case Study 2: A Simple Calculator using switch

This case study implements a simple calculator that performs addition, subtraction, multiplication, or division based on user input. 

 #include <stdio.h>

int main() {
    char operator;
    double num1, num2;

    printf("Enter an operator (+, -, *, /): ");
    scanf(" %c", &operator);  // Note the space before %c to consume any leading whitespace

    printf("Enter two numbers: ");
    scanf("%lf %lf", &num1, &num2);

    switch (operator) {
        case '+':
            printf("%.2lf + %.2lf = %.2lf\n", num1, num2, num1 + num2);
            break;
        case '-':
            printf("%.2lf - %.2lf = %.2lf\n", num1, num2, num1 - num2);
            break;
        case '*':
            printf("%.2lf * %.2lf = %.2lf\n", num1, num2, num1 * num2);
            break;
        case '/':
            if (num2 == 0) {
                printf("Error: Division by zero!\n");
            } else {
                printf("%.2lf / %.2lf = %.2lf\n", num1, num2, num1 / num2);
            }
            break;
        default:
            printf("Error: Invalid operator!\n");
    }

    return 0;
}

Nested `if` Statements: Determining Eligibility for a Loan

This example demonstrates nested `if` statements to determine loan eligibility based on age and income.

 #include <stdio.h>

int main() {
    int age;
    double income;

    printf("Enter your age: ");
    scanf("%d", &age);

    printf("Enter your annual income: ");
    scanf("%lf", &income);

    if (age >= 18) {
        if (income >= 30000.0) {
            printf("Congratulations! You are eligible for a loan.\n");
        } else {
            printf("Sorry, your income is not sufficient for a loan.\n");
        }
    } else {
        printf("Sorry, you must be at least 18 years old to apply for a loan.\n");
    }

    return 0;
}
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