Question

I had a test in my computer science course in which I was asked if any while loop can be replaced with a for loop. I put true. I guess the answer was false. My professor said that if you had a while loop in which you asked the user to input a certain value that had to be within a certain range and kept on iterating over the loop until the user inputted a value within the range that you wouldn't be able to do this with a for loop.

I however thought that any for loop can be written with a while loop and any while loop can be rewritten with a for loop. I think I may have even read something about this in my textbook but am unable to come up away with doing what my professor said with a for loop but believe that it's possible. Can anyone please come up with a way to do such a thing with a for loop?

for example a while loop

A=0;
while A<1
x=input('Enter a value');
if x>4 && x<10
A=1
else
end

this would force the user to enter a number between 4 and 10, not including 4 and 10, and would just keep on iterating over the loop until the user does.

Answer 1

The while loop exits whenever a user-specified condition is reached, in this case when x≤4 or x≥10.

A for loops exits (normally) when the stated number of cycles is reached, i.e. not an arbitrary user condition.

There are different ways to "misuse" the for loop.

A common one is to create an infinite for-loop and make an independent exit condition, such as:

for(i=0;i<1000;i=i){ // this line actually compiles and runs in Java
// enter x
if(x<=4 || x>=10)break;
}

Another way to "force" a while loop capability in languages such as Java, C and C++ would be:
int x=5;
for(int i=0;x>4&&x<10;i++){ // bad style!
if(i>2)x=0; // or an input for x
System.out.println("printing");
}

But these are exceptional uses of the for-loop and are considered bad style, even the syntax is correct.