Ineffective "if then" loop on my first program

ftmthy412 · #1 12-Sep-2007, 06:36

Hey all

Yesterday I tried to write my first program that included an "if then" loop with C++. I compiled it using g++, received some errors and fixed them, but in the process I somehow ended up rendering the loop ineffective. The program was just supposed to have you input two numbers and tell you which one was greater. The program is very small, so I'll post all the code because I'm not sure which parts are relevant.

Here's the code:

CPP / C++ / C Code:

//This program is to test an "if then" loop
//The user enters two numbers and the program says which is greater
#include <cstdio>
#include <cstdlib>
#include <iostream>
using namespace std;
int main()

{

//declare the variable

int nVariable;
//tell the user to enter a number

cout<< "Please enter a number  ";

//define the input

cin>> nVariable;

//tell the user to enter a second number

cout<< "Please enter a second number  ";

//declare the second variable and define the input

int nVariableTwo;

cin>> nVariableTwo;


//Here's the loop I'm having trouble with

	if (nVariable > nVariableTwo)
	{
cout<< nVariable; "is greater than"; nVariableTwo ;
	}
	else {cout<< nVariable; "is less than"; nVariableTwo; }

return 0;
}

For some reason the loop never "activates" and the program ends once the second number is given.
Does anyone know what's causing my problem?
Thanks a lot!

davekw7x · #2 12-Sep-2007, 07:51

Quote:

Originally Posted by ftmthy412

Hey all

Hey.

1. Your program doesn't have any loops.

2. When I run your program (after compiling with g++) I get things like the following:

Code:

Please enter a number  1
Please enter a second number  2
1

and

Code:

Please enter a number  2
Please enter a second number  1
2

Your code prints the value of the first variable.

Note that the following have no effect:

CPP / C++ / C Code:

        "is greater than";
        nVariableTwo;
.
.
.

        "is less than";
        nVariableTwo;

If you want to print stuff to cout, you can use cout << every time.

So

CPP / C++ / C Code:

        cout << nVariable;
        cout << " is greater than ";
        cout << nVariableTwo;
        cout << endl;

The '<<' operator is defined in such a way that any number of writes can be strung together:

CPP / C++ / C Code:

        cout << nVariable
             << " is less than "
             << nVariableTwo
             << endl;

Of course they could be all on the same line:

CPP / C++ / C Code:

        cout << nVariable << " is less than " << nVariableTwo << endl;

Output

Code:

Please enter a number  1
Please enter a second number  2
1 is less than 2

Code:

Please enter a number  2
Please enter a second number  1
2 is greater than 1

Regards,

Dave

ftmthy412 · #3 12-Sep-2007, 08:39

Thanks a lot! That fixed my problem, although my compiler still likes the c<< in front of every output.

davekw7x · #4 12-Sep-2007, 08:46

Quote:

Originally Posted by ftmthy412

my compiler still likes the c<< in front of every output

Well, as much as I like to anthropomorphize things, I am not a compiler, so I don't know what mine likes.

However...

Note the difference between the following:

1. A semicolon makes each line a complete statement. cout << begins each line

CPP / C++ / C Code:

        cout << nVariable;
        cout << " is greater than ";
        cout << nVariableTwo;
        cout << endl;

2. No semicolon except after the last line. All of the lines together make one statement:

CPP / C++ / C Code:

        cout << nVariable
             << " is less than "
             << nVariableTwo
             << endl;

So the effect of the second example is exactly the same as if I had written

CPP / C++ / C Code:

        cout << nVariable << " is less than " << nVariableTwo << endl;

All of these forms are equally acceptable to a C++ compiler. It's a matter of style. (Use the form that satisfies your human sensibilities.)

Details! Details! The devil is in the details!

Regards,

Dave

ftmthy412 · #5 12-Sep-2007, 09:17

Ah! You're right - I was overeager with my semi-colons.
Thanks.

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Ineffective "if then" loop on my first program

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