Python Program to Find Sum of Series 1-2+3-4+5...+N

In the previous article, we have discussed Python Program to Find Sum of Series 1+1/3+1/5+1/7+…..1/(N+2)

Given a number N and the task is to find the sum of the given series (1-2+3-4+5…+N) for the given number in Python.

Examples:

Example1:

Input:

Given Number = 20

Output:

The total sum of the series till the given number { 20 } =  -10

Example2:

Input:

Given Number = 7

Output:

The total sum of the series till the given number { 7 } =  4

Program to Find Sum of Series 1-2+3-4+5…+N in Python

Below are the ways to find the sum of the given series (1-2+3-4+5…+N) for the given number in Python:

Using For Loop (Static Input)
Using For loop (User Input)

Method #1: Using For Loop (Static Input)

Approach:

Give the number N as static input and store it in a variable.
Take a variable say resltsum which gives the sum of the given series till N and initialize its value to 0.
Loop from 1 to the given number using the for loop.
Inside the loop, check if the value of iterator modulus 2 is equal to zero(even condition) or not using the if conditional statement.
If the statement is True, then subtract the iterator value from the above-declared resltsum.
Store it in the same variable resltsum.
Else if the statement is False, then add the iterator value to the above-declared resltsum.
Store it in the same variable resltsum.
Print the resltsum value which is the result of the series till the given Number N.
The Exit of the Program.

Below is the implementation:

# Give the number N as static input and store it in a variable.
gvn_numb = 20
# Take a variable say resltsum which gives the sum of the given series till N and
# initialize its value to 0.
resltsum = 0
# Loop from 1 to the given number using the for loop.
for itr in range(1, gvn_numb+1):
    # Inside the loop, check if the value of iterator modulus 2 is equal to zero(even condition)
    # or not using the if conditional statement.
    if itr % 2 == 0:
      # If the statement is True, then subtract the iterator value from the above-declared
      # resltsum.
      # Store it in the same variable resltsum.
        resltsum -= itr
    else:
      # Else if the statement is False, then add the iterator value to the above-declared
      # resltsum.
      # Store it in the same variable resltsum.
        resltsum += itr
# Print the resltsum value which is the result of the series till the given Number N.
print(
    "The total sum of the series till the given number {", gvn_numb, "} = ", resltsum)

Output:

The total sum of the series till the given number { 20 } =  -10

Method #2: Using For loop (User Input)

Approach:

Give the number N as user input using the int(input()) function and store it in a variable.
Take a variable say resltsum which gives the sum of the given series till N and initialize its value to 0.
Loop from 1 to the given number using the for loop.
Inside the loop, check if the value of iterator modulus 2 is equal to zero(even condition) or not using the if conditional statement.
If the statement is True, then subtract the iterator value from the above-declared resltsum.
Store it in the same variable resltsum.
Else if the statement is False, then add the iterator value to the above-declared resltsum.
Store it in the same variable resltsum.
Print the resltsum value which is the result of the series till the given Number N.
The Exit of the Program.

Below is the implementation:

# Give the number N as user input using the int(input()) function and 
# store it in a variable.
gvn_numb = int(input("Enter some Random Number = "))
# Take a variable say resltsum which gives the sum of the given series till N and
# initialize its value to 0.
resltsum = 0
# Loop from 1 to the given number using the for loop.
for itr in range(1, gvn_numb+1):
    # Inside the loop, check if the value of iterator modulus 2 is equal to zero(even condition)
    # or not using the if conditional statement.
    if itr % 2 == 0:
      # If the statement is True, then subtract the iterator value from the above-declared
      # resltsum.
      # Store it in the same variable resltsum.
        resltsum -= itr
    else:
      # Else if the statement is False, then add the iterator value to the above-declared
      # resltsum.
      # Store it in the same variable resltsum.
        resltsum += itr
# Print the resltsum value which is the result of the series till the given Number N.
print(
    "The total sum of the series till the given number {", gvn_numb, "} = ", resltsum)

Output:

Enter some Random Number = 7
The total sum of the series till the given number { 7 } = 4

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