# Re: How to convert for, statements into while loops?

• From: "Dale Leavens" <dleavens@xxxxxxx>
• To: <programmingblind@xxxxxxxxxxxxx>
• Date: Sun, 18 Jul 2010 22:29:42 -0400

```Usually you don't want to do that. The reason is that they are intended for
different purposes. A "for" loop is intended where an operation is to be
performed a known number of times. If that number is to be changed by some
other aspect of the programme, for example if you wanted to work with a
multiplicand and another selected number of multipliers then you would input a
value for the last value, the 10, in your present "for" loop and in that way
alter the number of multiplications but it is still a known number of
operations.

A while loop is intended for use while a given condition is true. In this case
while you want to continue entering numbers to multiply.

You could of course still make a "while" loop achieve this with a statement
like:

while i < 11 and initializing i to 0 on entry to the loop but this is pretty
well pointless.

Now it is a matter of form but you should give your instruction to run or exit
the programme before entering the "while" loop, something like:

cout << "Press 'Y' to display a multiplication table, any other key to quit. ";
do {
cin >> anotherTable;

In this way the user can choose to abort the programme before it enters the
loop.

Not clear why you set up your "for" loop like you did.
for (int multiplier = -1; multiplier < 10; multiplier += 1)

Don't you want the multiplier to start at 1 and loop until it multiplies by 10
then quits? This looks like it begins as a negative 1 through 0 and on up to
10. I think it should be:

for (int multiplier = 1; multiplier < 11; multiplier++)

Note the double + signs after multiplier. This increments the integer by 1
after it is used so, after it becomes 10 and the loop executes it becomes 11
and when the loop reaches the top again it fails.

If you made that a while loop you would have to set multiplier to either 1
before entering the loop and still have to have a statement incrementing
multiplier by 1 immediately before the while statement, something like

multiplier++;
while (multiplier <11);

so that multiplier will fail the test when it reaches 11. It must do this at
the end of the loop.

Alternately you could set multiplier to 0 before entering the loop then
immediately increment it to 1 before acting on it. You have to be certain
though that it will be reset to 0 or 1 depending on your choice every time
before the loop is executed.

The "for" loop is the correct choice in that circumstance just as the while
loop is the correct choice for repeating the sequence because there is no
reasonable way to determine in advance if the user wants to continue inputting
numbers or how many times.

I hope this clarifies this for you.

Some languages also have a do -- until loop construct.

Dale Leavens.

----- Original Message -----
From: Jes
To: programmingblind@xxxxxxxxxxxxx
Sent: Sunday, July 18, 2010 9:38 PM
Subject: How to convert for, statements into while loops?

Hi all,
I got my program to work correctly, but now I want to learn how to convert
the pre test loop, the for statement, into a while loop.
***code**
//Ch8lab2.cpp
//Displays one or more multiplication tables
//Created/revised by Jes Smith on July 18, 2010

#include <iostream>

using std::cout;
using std::cin;
using std::endl;

int main()
{
//declare variables
char anotherTable = ' ';
int multiplicand = 0;
int product = 0;

do
{
//get the multiplicand
cout << "Enter the multiplicand: ";
cin >> multiplicand;

//display the multiplication table
for (int multiplier = -1; multiplier < 10; multiplier += 1)
{
product = multiplicand * multiplier;
cout << multiplicand << " * " << multiplier
<< " = " << product << endl;
} //end for

cout << endl;
cout << "Display another multiplication table? (Y/N) ";
cin >> anotherTable;
} while (toupper(anotherTable) == 'Y');
return 0;

} //end of function```
• Follow-Ups:
• References: