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

The program calculates the sum of the series 1-2+3-4+...-98+99.

The variable 'i' is used to iterate through the numbers from 1 to 99 (inclusive).

The variable 'sn' is used to keep track of the running total of the series.

The variable 'sign' is used to alternate the sign of each term in the series. It starts as positive (1) and is toggled between positive and negative with each iteration of the loop.

Inside the loop, the current value of 'i' is added to 'sn' with the appropriate sign (positive or negative) determined by the value of 'sign'.

Finally, the value of 'sn' is printed to the console as the result of the sum.