Explain the difference between for and while loop and give the suitable examples in c plus plus?

Answer 1

There is no actual difference; a for loop is just syntactic sugar for a while loop. Which you use depends largely upon which makes the most sense within the context of your source code. The for loop is clearly more flexible, but you will generally use a for loop whenever the number of iterations is known in advance, such as when counting iterations, whereas while loops are generally used whenever the number of iterations is unknown or infinite. Regardless, this has no effect on the efficiency of your code (the machine code maps almost directly, 1-to-1, with a while loop), it's just a question of which makes your code easier to read.

One useful property of a for loop is that you can declare and initialise a control variable in the initial expression. This renders the control variable local to the loop, which is something you cannot achieve with a while loop. This has no effect on the resultant machine code, but by scoping variables within a for loop you automatically enlist the help of the compiler to eliminate bugs.

It should be noted that the do-while loop is similar to a while loop, except that a do-while loop always executes its statements at least once, because the conditional expression is evaluated at the end of each iteration, rather than before each iteration as it is with a while loop. Again, a for loop can be used to achieve a do-while loop, however the do-while loop maps closely with the resultant machine code, and is generally much easier to read.