understanding the LCV in a Loop

[kromari]

How could I write a LCV to make my loop eventually false?

  #include <iostream>

using namespace std;

int main()
{
	int firstnum, secondnum;
	int sum;

	cout << "Enter two integers: ";
	cin >> firstnum >> secondnum;
	cout << endl;

	while (firstnum > secondnum)

		cout << "The first number must"
		<< "be less than the second number.";

	secondnum = secondnum * firstnum;

	return 0;
}

[chicofeo]

#include <iostream>
using std::cout;
using std::cin;
using std::endl;

int main()
{
    int firstnum, secondnum;
    int sum; // Are you going to use it?

    cout << "Enter two integers: ";
    cin >> firstnum >> secondnum;
    cout << endl;

    // If the first number is higher than
    // the second number, then it is true.
    // Otherwise, it is false.
    // Use enclosing braces {} to validate
    // the user input. Then, ask the user
    // to input the values again. 
    while (firstnum > secondnum)
    {
	   cout << "The first number must"
		  << "be less than the second number.";

	   cout << "Enter two integers: ";
	   cin >> firstnum >> secondnum;
	   cout << endl;
    }

    // Do you want to display the result? If yes,
    // then use cout.
    secondnum = secondnum * firstnum;

    return 0;
}

[kromari]

ok, I think I get it now, what you are doing is using the brackets to check if the statement is true. Right? I was under the impression that it had to be a true/false statement or something of the sort.

[keskiverto]

No. The syntax of while has two forms. There is either one statement after the condition (like you have), or a block of multiple statements within "brackets".

See http://www.cplusplus.com/doc/tutorial/control/

Your

while (firstnum > secondnum)
  cout << "The first number must" << "be less than the second number.";

is exactly the same as:

while (firstnum > secondnum)
{
  cout << "The first number must" << "be less than the second number.";
}

Nothing in that loop body can change the condition.


chicofeo's line 27 is in the loop's body and can change the condition.

[kromari]

alright, I'm on board now. The line 27 gives the user the chance to enter a correct input and therefore the gives the program the option to be true or false.

[chicofeo]

@kromari. Sorry for the confusion. keskiverto explained it better of what I meant. But, yeah, line 27 does what you say.