What does a count-controlled loop mean in programming?

Answer 1

A condition-controlled loop is one that has an indefinite number of iterations; its opposite is the count-controlled loop. Condition-controlled loops execute until some event occurs, which is usually user-initiated. For example, modern programs run an condition-controlled loop similar to the following:

while(GetMessage(message,hwnd,0,0)) { ... }

This loop continues to execute until there are no messages left (the WM_QUIT message is returned, which has a value of zero).

It is impossible to identify before execution the number of times such a loop will run, except during controlled tests, although you can easily identify what conditions will cause it to terminate.

Answer 2

A count-controlled loop is a condition-controlled loop with predictable number of iterations. The loop starts at some number (usually the topmost number or zero), then counts down until it reaches the limit (usually zero or the topmost number), at which point it exits the loop. The other common type starts at zero or one, and increments until it reaches a destination number.

Examples:

BASIC:

FOR X = 100 TO 1 STEP -1 ... NEXT X '100 iterations total, from 100 to 1.

Assembler (x86):

loopstart: mov cl,63 ; This is in hexadecimal, so 99 decimal.

...

loopnz loopstart ; Stop at zero, 100 iterations total.

C/C++:

for(int x = 0; x < 100; x++) { ... } // x goes from 0 to 99, 100 total iterations.