C++ Program To Find Largest Number Among Three Numbers Using If Else Statement

Finding the largest among three numbers is a common introductory programming problem that teaches fundamental conditional logic. This task requires comparing multiple values and determining which one holds the maximum.

In this article, you will learn how to write a C++ program to find the largest among three given numbers using various if-else statement constructs.

Problem Statement

The core problem is to accept three distinct numerical inputs from a user and then correctly identify and display the largest of these three numbers. This scenario often arises when you need to rank items, filter data based on magnitude, or make decisions in an application where a maximum value is critical. For instance, in a simple grading system, you might need to find the highest score among three tests.

Example

Consider three numbers: 15, 27, and 10. The program should identify 27 as the largest number.

Background & Knowledge Prerequisites

To understand this article, readers should have a basic grasp of:

• C++ Variables: How to declare and use integer or floating-point variables.
• Input/Output Operations: Using cin for input and cout for output.
• Conditional Statements: The fundamental concepts of if, else if, and else statements.
• Comparison Operators: Understanding operators like >, <, ==.

Use Cases or Case Studies

Identifying the largest among a small set of numbers is a building block for many real-world applications:

• Score Tracking: Determining the highest score among a small group of players in a game or students in a class.
• Sensor Data Analysis: Finding the peak reading from a set of three sensor measurements.
• Resource Allocation: In a simplified system, deciding which of three available resources has the highest capacity.
• Financial Comparisons: Comparing three investment returns to pick the best performer.
• User Preferences: Selecting a default option based on the highest preference score from three distinct choices.

Solution Approaches

We will explore two common approaches using if-else statements to solve this problem.

Approach 1: Using if-else if-else Ladder

This approach uses a sequence of if, else if, and else statements to check conditions one after another.

One-line summary: Compares numbers sequentially, executing the block corresponding to the first true condition.

Code Example:

// FindLargestAmongThree_IfElseIfElse
#include <iostream>
using namespace std;

int main() {
    // Step 1: Declare three integer variables to store the numbers.
    int num1, num2, num3;

    // Step 2: Prompt the user to enter three numbers.
    cout << "Enter three numbers: ";
    cin >> num1 >> num2 >> num3;

    // Step 3: Use if-else if-else ladder to find the largest number.
    if (num1 >= num2 && num1 >= num3) {
        cout << "The largest number is: " << num1 << endl;
    } else if (num2 >= num1 && num2 >= num3) {
        cout << "The largest number is: " << num2 << endl;
    } else {
        cout << "The largest number is: " << num3 << endl;
    }

    return 0;
}

Run

Sample Output:

Enter three numbers: 15 27 10
The largest number is: 27

Stepwise Explanation:

1. Variable Declaration: Three integer variables (num1, num2, num3) are declared to store the numbers provided by the user.
2. User Input: The program prompts the user to enter three numbers, which are then read into num1, num2, and num3 using cin.
3. First Condition: The if (num1 >= num2 && num1 >= num3) statement checks if num1 is greater than or equal to both num2 AND num3.
   • If this condition is true, num1 is the largest, and its value is printed.

1. Second Condition: If the first if condition is false, the program moves to the else if (num2 >= num1 && num2 >= num3) statement. This checks if num2 is greater than or equal to both num1 AND num3.
   • If this condition is true, num2 is the largest, and its value is printed.

1. Default Case: If both the if and else if conditions are false, it implies that num3 must be the largest number (as it wasn't smaller than num1 and num2 in their respective checks). The final else block executes, printing num3 as the largest.

Approach 2: Using Nested if-else Statements

This approach involves placing if-else statements inside other if-else statements, creating a hierarchical comparison.

One-line summary: Nests conditional checks to progressively narrow down the largest number.

Code Example:

// FindLargestAmongThree_NestedIfElse
#include <iostream>
using namespace std;

int main() {
    // Step 1: Declare three integer variables.
    int num1, num2, num3;

    // Step 2: Prompt for and read three numbers.
    cout << "Enter three numbers: ";
    cin >> num1 >> num2 >> num3;

    // Step 3: Use nested if-else to find the largest number.
    if (num1 >= num2) {
        // If num1 is greater than or equal to num2, compare num1 with num3.
        if (num1 >= num3) {
            cout << "The largest number is: " << num1 << endl;
        } else {
            // If num1 < num3, then num3 must be the largest.
            cout << "The largest number is: " << num3 << endl;
        }
    } else { // This means num2 > num1
        // If num2 is greater than num1, compare num2 with num3.
        if (num2 >= num3) {
            cout << "The largest number is: " << num2 << endl;
        } else {
            // If num2 < num3, then num3 must be the largest.
            cout << "The largest number is: " << num3 << endl;
        }
    }

    return 0;
}

Run

Sample Output:

Enter three numbers: 15 27 10
The largest number is: 27

Stepwise Explanation:

1. Variable Declaration and Input: Similar to the previous approach, variables are declared, and numbers are taken as input.
2. Initial Comparison (num1 vs num2):
   • The outer if (num1 >= num2) checks if num1 is greater than or equal to num2.

1. If num1 >= num2 (True Path):
   • It enters the first inner if block. Now, we know num1 is either the largest or num3 is.

1. If num1 >= num2 (False Path - else):
   • This else block executes when num2 is strictly greater than num1. Now, we know num2 is either the largest or num3 is.

Conclusion

Finding the largest number among three is a foundational exercise in programming logic. Both the if-else if-else ladder and nested if-else statements effectively solve this problem by systematically comparing the numbers. The choice between these approaches often depends on personal preference and the specific readability requirements of a project. The if-else if-else ladder is generally considered more straightforward for this specific problem due to its linear flow, while nested if-else demonstrates a different way to structure conditional logic.

Summary

• The problem involves comparing three numbers to identify the maximum.
• if-else if-else Ladder: Provides a sequential, clear way to check multiple conditions until one is met.
• Nested if-else: Organizes comparisons hierarchically, progressively narrowing down the possibilities.
• Both methods rely on fundamental C++ conditional statements and comparison operators.
• Understanding these basic conditional structures is crucial for building more complex decision-making logic in programs.