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

Finding the largest among three numbers is a common programming problem that introduces fundamental conditional logic. This article will guide you through creating a C program to solve this using if statements.

Problem Statement

The core problem involves comparing three distinct numerical values and identifying which one holds the maximum value. This task is fundamental in various computational scenarios, from simple data analysis to complex algorithm design, where determining the peak value is crucial.

Example

Consider three numbers: 10, 25, and 15. The program should correctly identify 25 as the largest number.

Background & Knowledge Prerequisites

To understand and implement the C programs in this article, you should have a basic understanding of:

• C Language Basics: Variables, data types (e.g., int, float), and basic input/output operations.
• Conditional Statements: How if, else if, and else statements work to control program flow based on conditions.
• Operators: Comparison operators (>, <, >=, <=, ==, !=) and logical operators (&& for AND, || for OR).

Use Cases or Case Studies

Identifying the largest value among a small set of numbers has several practical applications:

• Data Validation: Ensuring an input value falls within a permissible range, or selecting the highest priority item.
• Game Development: Determining the highest score in a local leaderboard or the strongest character attribute.
• Financial Analysis: Finding the highest stock price, best-performing asset, or maximum profit from a small sample.
• Sensor Readings: Identifying the peak reading from three different sensors monitoring a single environmental factor.
• Resource Allocation: Deciding which of three available resources has the most capacity or is least utilized.

Solution Approaches

Here, we will explore two common methods using if statements to find the largest of three numbers.

Approach 1: Using if-else if-else Ladder

This approach uses a sequence of if, else if, and else statements to check conditions sequentially.

• Summary: Compares the first number with the other two, then the second with the third, and finally assumes the third is the largest if previous conditions are false.

// Find Largest Among Three (if-else if-else)
#include <stdio.h>

int main() {
    int num1, num2, num3;

    // Step 1: Prompt user for input
    printf("Enter three numbers: ");

    // Step 2: Read the three numbers from user
    scanf("%d %d %d", &num1, &num2, &num3);

    // Step 3: Use if-else if-else ladder to find the largest
    if (num1 >= num2 && num1 >= num3) {
        printf("%d is the largest number.\\n", num1);
    } else if (num2 >= num1 && num2 >= num3) {
        printf("%d is the largest number.\\n", num2);
    } else {
        printf("%d is the largest number.\\n", num3);
    }

    return 0;
}

Run

• Sample Output:

  Enter three numbers: 10 25 15
  25 is the largest number.

Enter three numbers: 50 10 30
    50 is the largest number.

Enter three numbers: 5 12 80
    80 is the largest number.

• Stepwise Explanation:

1. The program starts by declaring three integer variables: num1, num2, and num3.
2. It prompts the user to enter three numbers and then reads these values using scanf.
3. The first if condition (num1 >= num2 && num1 >= num3) checks if num1 is greater than or equal to both num2 and num3. If true, num1 is the largest.
4. If the first condition is false, the else if condition (num2 >= num1 && num2 >= num3) is evaluated. This checks if num2 is greater than or equal to both num1 and num3. If true, num2 is the largest.
5. If both if and else if conditions are false, it means num3 must be the largest, so the else block executes, printing num3.

Approach 2: Using Nested if Statements

This approach uses if statements embedded within other if statements.

• Summary: First determines the larger of the first two numbers, then compares that result with the third number.

// Find Largest Among Three (Nested if)
#include <stdio.h>

int main() {
    int num1, num2, num3, largest;

    // Step 1: Prompt user for input
    printf("Enter three numbers: ");

    // Step 2: Read the three numbers from user
    scanf("%d %d %d", &num1, &num2, &num3);

    // Step 3: Use nested if statements
    if (num1 >= num2) {
        // If num1 is greater than or equal to num2
        if (num1 >= num3) {
            // If num1 is also greater than or equal to num3
            largest = num1;
        } else {
            // Else, num3 must be greater than num1 (and num1 >= num2 is true)
            largest = num3;
        }
    } else {
        // If num2 is greater than num1
        if (num2 >= num3) {
            // If num2 is also greater than or equal to num3
            largest = num2;
        } else {
            // Else, num3 must be greater than num2 (and num2 > num1 is true)
            largest = num3;
        }
    }

    // Step 4: Print the largest number
    printf("%d is the largest number.\\n", largest);

    return 0;
}

Run

• Sample Output:

  Enter three numbers: 10 25 15
  25 is the largest number.

Enter three numbers: 50 10 30
    50 is the largest number.

Enter three numbers: 5 12 80
    80 is the largest number.

• Stepwise Explanation:

1. The program declares three integer variables num1, num2, num3 for input, and largest to store the result.
2. It takes three numbers as input from the user.
3. The outermost if (num1 >= num2) checks if num1 is greater than or equal to num2.

• If true, it enters the first nested block. Here, if (num1 >= num3) then checks if num1 is also greater than or equal to num3. If both true, num1 is the largest. Otherwise, num3 is the largest.
• If false (meaning num2 is greater than num1), it enters the else block. Here, if (num2 >= num3) checks if num2 is greater than or equal to num3. If true, num2 is the largest. Otherwise, num3 is the largest.

1. Finally, the program prints the value stored in the largest variable.

Conclusion

This article demonstrated how to find the largest among three numbers in C using two different structures of if statements: the if-else if-else ladder and nested if statements. Both approaches effectively solve the problem by applying conditional logic to compare the numbers and identify the maximum value. Understanding these fundamental conditional constructs is crucial for writing more complex programs that make decisions based on varying inputs.

Summary

• The problem involves identifying the maximum value among three given numbers.
• Basic C knowledge, including variables, input/output, and if statements, is required.
• Practical applications range from data validation to game development and financial analysis.
• Approach 1 (if-else if-else ladder): Compares each number against the others sequentially using logical AND (&&).
• Approach 2 (Nested if statements): Compares two numbers first, then compares the larger of those with the third.
• Both methods provide a clear solution to the problem, reinforcing the use of conditional programming logic.