Infinite Loop

[rsh0117]

I cannot pinpoint why the infinite loop occurs. What I have makes sense in my head but not to the compiler

sum = 0
incr = 1/num
for (val = 20.0; val <= 21.0; val += incr) 
   {
      cout << val << " ";
      sum += incr;
   }

Assume all variables are defined as types and let's say num is 4
but my output is
20 20 20 20 20 20 ...

with 4 as num , the output is to be
20 20.25 20.5 20.75 21

[firedraco]

What is the type of incr and num?

[rsh0117]

int num
float incr

[Exiled]

How are you using num? What is it equal to?

[rsh0117]

num is equal to some positive even number; for the sake, I'm testing 4

[rsh0117]

oh yeah, this is an assignment so don't just give me the code but please point me in the right direction

[MathematicsFanatic]

When you are doing 1 / num, num is an integer and thus you are doing integer division resulting in an integer value of 0 (assuming num = 4). If you want your program to calculate the actual value, num needs to be a float as well.

[rsh0117]

but when I change num to a float, it messes up this loop:

  if(num % 2 == 0 && num > 0 && num != 0)
      cout << "The number " << num << " is even!" << endl << endl;
   else 
      cout << "The number is not a positive even number." << endl;
   } while (num % 2 !=0 || num <=0);

[MathematicsFanatic]

Well we didn't see that earlier did we? :D

May I suggest doing something like int num1 and float num2. Then have something like num1 = num2.

Also, in your if statement, having it say num != 0 right after num > 0 is redundant.

[rsh0117]

No you may not, cuz it didn't work :p
and it is redundant, but when I tested 0, it went right through the loop

[MathematicsFanatic]

Can you post the entire code please so we can see what your program is trying to do?

[rsh0117]

it actually did work, I just ~sigh~

/*
Randall Hall
CSCE 1020.302
Lab 09
[e-mail]

*/
#include <iostream>
int main() {
   float val, sum, incr, num2;
   int num1;
   num1 = num2;

   cout << "CSCE 1020 Lab 9\tRandall Hall\[e-mail]" << endl;
   cout << "\n";
   do {
   cout << "Enter an even number: ";
   cin >> num1;
   if(num1 % 2 == 0 && num1 > 0 && num1 != 0)
      cout << "The number " << num1 << " is even!" << endl << endl;
   else 
      cout << "The number is not a positive even number." << endl;
   } while (num1 % 2 !=0 || num1 <=0);
   sum = 0;
   incr = 1/num2;
   for (val = 20.0; val >= 21.0; val += incr) 
   {
      cout << val << " ";
      sum += incr;
   }
   cout << "The sum is " << sum << endl;
   return 0;
}

Let's say you input 4
output supposed to be
20 20.25 20.5 20.75 21
The sum is: [sum of those numbers]

[MathematicsFanatic]

Your for loop to calculate sum does not even run, try changing val >= 21.0 to val <= 21.0. :D

[rsh0117]

I changed the for loop to a do while:

 do {
   cout << val << " ";
   sum += val;
   val += incr;
   } while (num2 < 21.0 && num2 > 20.0);

[MathematicsFanatic]

Here we go! The reasons why the program wasn't working are as follows. First, when we declare that num1 = num2, what ever random value num2 had is stored in num1. This is not good! We need to declare num2 = num1 after we have defined what num1 is. Secondly, we need to do something with sum += incr; Since incr = .25, sum is going to be .25 + .25 + .25 + .25 = 1. Change sum += incr; to something more meaningful.

CSCE 1020 Lab 9 Randall Hall    [e-mail]

Enter an even number: 4
The number 4 is even!

20 20.25 20.5 20.75 21 The sum is 102.5

Process returned 0 (0x0)   execution time : 1.314 s
Press any key to continue.

[GFreak45]

the original issue was that 1/num is an integer value because 1 is an int, you need to do 1.0 so the compiler knows thats supposed to be a float

dont know if this input shed any light as i didnt read the whole thread

[rsh0117]

what do you mean by change sum += incr; to something more meaningful?

[rsh0117]

GFreak45, my friend suggested that also but it didn't do anything, well it did nut nothing that I could immediately see

[Pravesh Koirala]

sum = 0;
incr = 1/(float)num; // or incr = 1./num
for (val = 20.0; val <= 21.0; val += incr) 
   {
      cout << val << " ";
      sum += incr;
   }

[Pravesh Koirala]

And by the way, haven't you guys ever heard about something called Debugging? Like step over, step into, step out, call stack, watches, breakpoints? None at all?