Ways to evaluate loops quickly

Need some help with a formula:

What is the quick formula/way for evaluating no. of times a loop will be processed without actually evaluating the loop?

I was told this:

(Final - Initial)/Step

final is final value

initial is initial value

step is the increment value

for <= condition increment final by one

Example 1

Code:

int i= 5;

while (i <= 10)

{

cout << "hi" <<endl;

i++;

}

using formula (11- 5)/1 = 6 times which is correct

but

with Example 2

Code:

int count = 1;

int num = 25;

while (count < 25)

{

num = num - 1;

count++;

}

cout <<count << num << endl

would print 25 and 1.

Formula (25- 1)/1 =24 times which would make the formula found not work for all cases.

Do any of you the correct formula for this?

FYI: Asking here first- will ask fellow math instructors later... :p

mrc