Confusing in [for loop] topic

[Sherine]

You are using the wrong term. Your program has two loops. The outer loop ITERATES 4 times: (0, 1, 2, 3). The inner loop iterates 16 times: 4x(0, 1, 2, 3). Some would also say (correctly) that the inner loop ITERATES 4 times and this is repeated 4 times.

Add a print statement to the loop:

x = 0
n = 5
for i in range(1, n):
    for j in range(1, n):
        if((i+j) == 2):
            x = x + 2
        if((i+j) == 3):
            x = x + 3
        if((i+j) == 4):
            x = x + 4
        v
print(x)

Output:
1 1 2 2  <- Three changes while i = 1
1 2 3 5 <-
1 3 4 9 <-
1 4 5 9 
2 1 3 12 <- Two changes while i = 2
2 2 4 16 <-
2 3 5 16
2 4 6 16
3 1 4 20 <- Only one change while i = 3
3 2 5 20
3 3 6 20
3 4 7 20
4 1 5 20 <- No changes while i = 4
4 2 6 20
4 3 7 20
4 4 8 20

Focusing on the last two columns you can see that the value of the last column (x) only changes when the value in the 3rd column (i+j) is 2, 3 or 4.

I would explain this as "x only increases if the value of i+j is 2, 3 or 4", but if you wanted to describe it using loops you could say:

When i is 1 you add values for j = 1, 2 and 3 (2, 3, 4)
When i is 2 you add values for j = 1 and 2 (3, 4)
When i is 3 you add values for j = 1 (4)
When i is 4 you don't add any values
x = 2 + 2*3 + 3*4 = 2 + 6 + 12 = 20

Thank you for your reply.
I understood with your statement

print(i, j, i+j, x)

,
this output make me clear.

This "x = 2 + 2*3 + 3*4 = 2 + 6 + 12 = 20" calculation I can't understand.
But it's okay, I really appreciate to your statement, let me know how this statement work.

Thanks