Explain process

[Cannor]

Can someone do me the favor of explaining how this output is 4? Thanks in advance. Struggling with the basics ain't fun!

#include "stdafx.h"
#include <iostream>

using namespace std;

int main() {
	int sum = 0; // variable declared
	for (int i = 1;i < 10;i += 2) { //init,argument,?
		if (10 / i == 2) //statement
			break; // exits the for loop?
		sum += i; // calculates the sum?
	}
	cout << sum; // outputs 4
	system("pause"); // "press any key to continue..."
}

[TheIdeasMan]

Hi,

You can work this out yourself by adding some extra cout statements to see what the values of various variables or expressions are are each time:

#include "stdafx.h"
#include <iostream>

using namespace std;

int main() {
	int sum = 0; // variable declared
	for (int i = 1;i < 10;i += 2) { //init,argument,?
                cout << "variable i is " << i <<"\n";
		if (10 / i == 2) { // always uses braces even when there is 1 statement
                        // put cout statement here, the value of 10 / i
			break; // exits the for loop? // yes
                }
		sum += i; // calculates the sum?
                // put cout statement here to print value of sum variable
	}
	cout << sum; // outputs 4
	system("pause"); // "press any key to continue..."
}

Hope this helps a little bit :+)

[E0p9LyTq]

#include <iostream>

int main()
{
   int sum = 0;
   
   for (int i = 1; i < 10; i += 2)
   { 
      std::cout << "i: " << i << ", sum: " << sum << "\n";

      if (10 / i == 2)  //<--- what is 10 / 5?
      {
         break;
      }

      sum += i;
      std::cout << "\tnew sum: " << sum << "\n";
   }

   std::cout << "\nfinal sum: " << sum << "\n";
}

i: 1, sum: 0
        new sum: 1
i: 3, sum: 1
        new sum: 4
i: 5, sum: 4

final sum: 4

[Cannor]

Thank you!

Now whether I did it properly or not remains to be *heard* but as I understand it when compiling is that "i" adds up to become 5, then 10 / 5 == 2,

and then sum += i; will be 2 + 2? I don't grasp yet though, how i may be 2 now if the for loop is not taken into account again.

The more I think about this the more stupid I feel this is on my part, I'll just keep asking rookie questions :P

#include "stdafx.h"
#include <iostream>

using namespace std;

int main() {
	int sum = 0; // variable declared
	for (int i = 1;i < 10;i += 2) { //init,condition,increment
		cout << "variable i is " << i << "\n";
		if (10 / i == 2) { // always uses braces even when there is 1 statement
			cout << 10 / i << endl;			   // put cout statement here, the value of 10 / i
			break; // exits the for loop
		}
		sum += i; // calculates the sum?
		cout << sum << endl;		  // put cout statement here to print value of sum variable
	}
	cout << sum << endl; // outputs 4
	system("pause"); // "press any key to continue..."
}

[Cannor]

Missed your reply at first furryguy, haha thanks! I'll be understanding this now =) I guess never mind my bad code above

[TheIdeasMan]

Hi,

Put some text in your cout statement, so you know what is what. It is confusing otherwise - because of the if statement.

cout << "variable i is " << i << "\n";

[TheIdeasMan]

A more sophisticated way is to use an actual debugger. Hopefully there is a GUI version in your IDE. Set up a watch list of variables to keep an eye on, then step through the code 1 line at a time, see how the variables values change and deduce where it all goes wrong (or see what is happening).

This will be very useful once your programs are bigger - it's a pain to put cout statements everywhere, then have to delete them all at the end. Will also save you days of staring at code wondering why it's wrong.