Finding the largest of three numbers is a classic exercise for learning if-elif-else statements and comparison operators. In this lesson, you will solve it with conditions, and then with Python’s built-in max() function.

Run the code in our online Python compiler. The compiler does not take keyboard input, so the examples use fixed values.

 

The logic

A number is the largest if it is greater than or equal to both of the others.

  1. If a is greater than or equal to b and c, then a is the largest.
  2. Otherwise, if b is greater than or equal to a and c, then b is the largest.
  3. Otherwise, c is the largest.

We use “greater than or equal to” (>=), so the program also works when two or all three numbers are equal.

 

Program 1: using if-elif-else

def largest(a, b, c):
    if a >= b and a >= c:
        return a
    elif b >= a and b >= c:
        return b
    else:
        return c

print(largest(10, 25, 7))
print(largest(5, 5, 3))
print(largest(-1, -5, -3))
print(largest(4, 4, 4))

Output:

25
5
-1
4

How it works

Take largest(10, 25, 7). The first check asks whether 10 >= 25. That is False, so the program moves on. The second check asks whether 25 >= 10 and 25 >= 7. Both are True, so it returns 25.

The and operator is True only when both conditions are True.

 

Program 2: using the built-in max() function

Python can do this in one line:

print(max(10, 25, 7))
print(max([10, 25, 7]))
print(min(10, 25, 7))

Output:

25
25
7

max() takes any number of values, or a single list. min() works the same way and gives the smallest value.

 

Program 3: using sorted()

numbers = [10, 25, 7]
print(sorted(numbers)[-1])

Output:

25

sorted() puts the numbers in ascending order, and the index -1 picks the last, which is the largest. This is slower than max(), but it is useful if you also want the second largest (use [-2]).

 

Program 4: the largest of any number of values

The if-elif-else program works for exactly three numbers. This loop works for any list:

numbers = [4, 19, 7, 25, 11]
biggest = numbers[0]

for n in numbers:
    if n > biggest:
        biggest = n

print(biggest)

Output:

25

The program starts with the first number as the largest so far, and updates it whenever it finds a bigger one.

 

Which method should you use?

Method

Best for

if-elif-else

Learning conditions, and exam answers

max()

Real programs

sorted()

Also finding the second or third largest

Loop

Understanding how max() works inside

 

Take the numbers from the user (on your computer)

a = float(input('Enter the first number: '))
b = float(input('Enter the second number: '))
c = float(input('Enter the third number: '))
print('The largest number is', largest(a, b, c))

Our online compiler does not support input() yet, so use fixed values there.

 

Common mistakes

  • Using > instead of >=. The program then fails when two numbers are equal and the largest.
  • Forgetting the and operator. Writing a >= b >= c can give a wrong or confusing result.
  • Naming a variable max. This hides the built-in max() function, and later calls fail.

 

Practice questions

  1. Find the smallest of three numbers using if-elif-else.
  2. Find the second largest of three numbers.
  3. Find the largest and smallest numbers in a list without using max() and min().
  4. Print the three numbers in descending order.

 

FAQs

How do you find the largest of three numbers in Python?

Use max(a, b, c), or compare the numbers with if-elif-else.

What if two numbers are equal?

The program above still works, because it uses >=. If the two equal numbers are the largest, it returns that value.

Can I find the largest of more than three numbers?

Yes. Use max() with a list, or use the loop program above.

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