As we have declared another variable of int data type, so the variables of same data type can be declared in one line. int sum, number; Going back to our problem, we need to sum up all the integers from 1 to 1000. Our first integer is 1. The variable number is to be used to store integers, so we will initialize it by 1 as our first integer is 1: number = 1; Now we have two variables- sum and number. That means we have two memory locations labeled as sum and number which will be used to store sum of integers and integers respectively. In the variable sum, we have to add all the integers from 1 to 1000. So we will add the value of variable number into variable sum, till the time the value of number becomes 1000. So when the value of number becomes 1000, we will stop adding integers into sum. It will become the condition of our while loop. We can say sum the integers until integer becomes 1000. In C language, this condition can be written as: while ( number <= 1000 ) { ………Action ……… } The above condition means, 'perform the action until the number is 1000 or less than 1000'. What will be the Action? Add the number, the value of number is 1 initially, into sum. This is a very simple statement: sum = sum + number; Let’s analyze the above statement carefully. We did not write sum = number; as this statement will replace the contents of sum and the previous value of sum will be wasted as this is an assignment statement. What we did? We added the contents of sum and contents of number first (i.e. 0 + 1) and then stored the result of this (i.e. 1) to the sum.
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