We have to calculate the sum of first 1000 integers by taking a variable sum of type int. It is a good programming practice to initialize the variable before using it. Here, we initialize the variable sum with zero. int sum = 0; Now we get the first integer i.e. 1. We add this to the sum (sum becomes 0 + 1 = 1). Now get the next integer which can be obtained by adding 1 to the previous integer i.e. 2 and add it to the sum (sum becomes 1 + 2 = 3). Get the next integer by adding 1 to the previous integer and add it to the sum (sum becomes 3 + 3 = 6) and so on. This way, we get the next integer by adding 1 to the previous integer and the new integer to the sum. It is obvious that we are repeating this procedure again and again i.e. adding 1 to the previous integer and add this new integer to the sum. So we need some repetition structure in the programming language. There are many looping constructs in C Language. The repetition structure we are discussing in this lecture is 'while loop structure'. ‘while’ is also a key word of 'C' so it cannot be used as a variable name. While means, 'do it until the condition is true'. The use of while construct can be helpful in repeating a set of instructions under some condition. We can also use curly braces with while just like we used with if. If we omit to use the braces with while construct, then only one statement after while will be repeatedly executed. For good programming practices, always use braces with while irrespective of the number of statements in while block. The code will also be indented inside the while block as Indentation makes the code easy to understand.
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