C Program to Calculate the Alternating Series 1-2+3-4+...+99

The program calculates the sum of the alternating series 1-2+3-4+...+99.

The variable 'i' is used as the index for the loop, starting at 1 and going up to 99 (not including 100).

The variable 'sn' (short for 'sum n') is used to keep track of the sum of the series. It starts at 0 and is updated in each iteration of the loop by adding the current value of the series term ('i') multiplied by the sign (-1 or 1).

The variable 'sign' is used to alternate the sign of each term in the series. It starts at 1 and is changed to -1 (or vice versa) in each iteration of the loop.

After the loop has finished, the final value of 'sn' is printed to the console.