If…Then…Else

In the previous section we looked at the If…Then statement that is used for making a decision. When using the If…Then statement a section of code is performed only if the Boolean statement is true. If the Boolean statement is false, nothing happens. In some situations, if the Boolean statement is false and the section of code is not performed, you would like an alternative piece of code to be performed instead. In this case an optional Else statement can be used. The If…Then…Else statement (in most computer programming languages), takes the generic form of:

IF (Boolean expression) THEN

statements to be performed …

ELSE

alternate statements to be performed …

ENDIF

In the previous example of asking the user how many students were in the class, you might have noticed that the user was given no feedback if there were 30 or fewer students. This can add confusion for the user; they might be unsure if the program worked correctly.

An example of what this would look like using an If .. Then .. Else statement is shown below:

Top-Down Design for If…Then…Else statement

Flowchart for If…Then…Else statement

Pseudocode for If…Then…Else statement

GET number_of_students

IF (number_of_students > 30) THEN

SHOW “Too many students!”

ELSE

SHOW “Not too many students.”

ENDIF

Code for If…Then…Else statement

C

C++

C#

Go

Java

JavaScript

Python

// Copyright (c) 2020 Mr. Coxall All rights reserved.
//
// Created by: Mr. Coxall
// Created on: Sep 2020
// This program checks if there is over 30 students

#include <stdio.h>

int main() {
    // this function checks if there is over 30 students
    const int MAX_STUDENT_NUMBER = 30;
    int numberOfStudents;

    // input
    printf("Enter the number of students: ");
    scanf("%d", &numberOfStudents);

    // process and output
    if (numberOfStudents > MAX_STUDENT_NUMBER) {
        printf("Too many students!\n");
    } else {
        printf("Not too many students.\n");
    }

    printf("\nDone.\n");
    return 0;
}

// Copyright (c) 2020 Mr. Coxall All rights reserved.
//
// Created by: Mr. Coxall
// Created on: Sep 2020
// This program checks if there is over 30 students

#include <iostream>

int main() {
    // this function checks if there is over 30 students
    const int MAX_STUDENT_NUMBER = 30;
    int numberOfStudents;

    // input
    std::cout << "Enter the number of students: ";
    std::cin >> numberOfStudents;

    // process and output
    if (numberOfStudents > MAX_STUDENT_NUMBER) {
        std::cout << "Too many students!\n";
    } else {
        std::cout << "Not too many students.\n";
    }

    std::cout << "\nDone." << std::endl;
}

/* Created by: Mr. Coxall
 * Created on: Sep 2020
 * This program checks if there is over 30 students
*/

using System;

/*
 * The Program class
*/
class Program {
    static void Main() {
        // this function checks if there is over 30 students
        const int MAX_STUDENT_NUMBER = 30;
        int numberOfStudents;

        // input
        Console.Write("Enter the number of students: ");
        numberOfStudents = Convert.ToInt32(Console.ReadLine());

        // process and output
        if (numberOfStudents > MAX_STUDENT_NUMBER) {
            Console.WriteLine("Too many students!");
        } else {
            Console.WriteLine("Not too many students.");
        }

        Console.WriteLine("\nDone.");
    }
}

/**
 * Created by: Mr. Coxall
 * Created on: Sep 2020
 * This program checks if there is over 30 students
 */

package main

import "fmt"

func main() {
	// this function checks if there is over 30 students
	const maxStudentNumber int = 30
	var numberOfStudents int

	// input
	fmt.Print("Enter the number of students: ")
	fmt.Scan(&numberOfStudents)

	// process and output
	if numberOfStudents > maxStudentNumber {
		fmt.Println("Too many students!")
	} else {
		fmt.Println("Not too many students.")
	}

	fmt.Println("\nDone.")
}

/*
 * This program checks if there is over 30 students
 *
 * @author  Mr Coxall
 * @version 1.0
 * @since   2020-09-01
 */

import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    // this function checks if there is over 30 students
    final int MAX_STUDENT_NUMBER = 30;
    int numberOfStudents;

    // input
    Scanner input = new Scanner(System.in);
    System.out.print("Enter the number of students: ");
    numberOfStudents = input.nextInt();

    // process and output
    if (numberOfStudents > MAX_STUDENT_NUMBER) {
      System.out.println("Too many students!");
    } else {
      System.out.println("Not too many students.");
    }

    System.out.println("\nDone.");
  }
}

/* Created by: Mr. Coxall
 * Created on: Sep 2020
 * This program checks if there is over 30 students
*/

const prompt = require('prompt-sync')()
const MAX_STUDENT_NUMBER = 30

// input
const numberOfStudents = parseInt(prompt('Enter the number of students: '))

// process and output
if (numberOfStudents > MAX_STUDENT_NUMBER) {
    console.log("Too many students!")
} else {
    console.log("Not too many students.")
}

console.log("\nDone.")

constants.py

#!/usr/bin/env python3
"""
Created by: Mr. Coxall
Created on: Sep 2020
This module holds constants
"""

# constant definition
MAX_STUDENT_NUMBER = 30

main.py

#!/usr/bin/env python3
"""
Created by: Mr. Coxall
Created on: Sep 2020
This module checks if there is over 30 students
"""


from constants import MAX_STUDENT_NUMBER


def main() -> None:
    """The main() function checks if over 30 students, returns None."""

    # input
    number_of_students = int(input("Enter the number of students: "))

    # process and output
    if number_of_students > MAX_STUDENT_NUMBER:
        print("Too many students!")
    else:
        print("Not too many students.")

    print("\nDone.")


if __name__ == "__main__":
    main()

Example Output