for loop to add the first n numbers

Okay, let’s use a for loop to add up the first ’n’ numbers! 🤩 This is a classic programming task that helps you see how loops can automate repetition for calculations.

Remember how we introduced the for loop? It’s great for when you want to do something a specific number of times or go through items in a sequence ✨. To add the first ’n’ numbers, we know exactly how many times we need to add: ’n’ times!

Here’s the goal: We want to calculate the sum, like 0 + 1 + 2 + 3 + … + (n-1) (if we start from 0) or 1 + 2 + 3 + … + n (if we start from 1). Let’s follow an example from the sources which adds 0 through 9, resulting in 45.

To do this with a for loop, we need two main things:

1. An accumulator variable: This is a variable that will start at 0 and “accumulate” or collect the sum as we go along. Think of it like an empty bucket 🪣 that you drop numbers into one by one. We often call this variable sum or answer.
2. A way to generate the numbers we want to add (0, 1, 2, … up to n-1 or 1, 2, … up to n). The range() function is perfect for this! 🔢.

Here’s the basic code structure based on the sources:

# 1. Initialize the accumulator bucket! 🪣
answer = 0 # Start the sum at zero

# 2. Use a for loop with range() to get the numbers 🔢
# range(10) gives numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
for i in range(10):
    # 3. Inside the loop, add the current number (i) to the accumulator
    answer = answer + i # Or the shorthand: answer += i
    # This line runs for each number produced by range()

# 4. After the loop finishes (no more numbers in the range),
#    the 'answer' variable holds the final sum. 🎉
print(answer) # Display the result

Let’s trace what happens step-by-step when the loop runs for range(10):

• Before the loop: answer is 0.
• Loop starts. The for loop gives the first number from range(10) to the variable i.
• Iteration 1: i becomes 0.
  • answer = answer + i becomes answer = 0 + 0, so answer is now 0.
• Iteration 2: i becomes 1.
  • answer = answer + i becomes answer = 0 + 1, so answer is now 1.
• Iteration 3: i becomes 2.
  • answer = answer + i becomes answer = 1 + 2, so answer is now 3.
• Iteration 4: i becomes 3.
  • answer = answer + i becomes answer = 3 + 3, so answer is now 6.
• Iteration 5: i becomes 4.
  • answer = answer + i becomes answer = 6 + 4, so answer is now 10.
• Iteration 6: i becomes 5.
  • answer = answer + i becomes answer = 10 + 5, so answer is now 15.
• Iteration 7: i becomes 6.
  • answer = answer + i becomes answer = 15 + 6, so answer is now 21.
• Iteration 8: i becomes 7.
  • answer = answer + i becomes answer = 21 + 7, so answer is now 28.
• Iteration 9: i becomes 8.
  • answer = answer + i becomes answer = 28 + 8, so answer is now 36.
• Iteration 10: i becomes 9.
  • answer = answer + i becomes answer = 36 + 9, so answer is now 45.
• range(10) is exhausted (it only goes up to 9). The loop finishes.
• The code after the loop runs. print(answer) displays 45! ✅.

This demonstrates how the for loop, combined with range(), makes adding a sequence of numbers much easier and more efficient than doing it manually. It’s a fundamental pattern you’ll use frequently in programming! 💪😊