4 replies to this topic

[jackson6612]

Hi :)

My elementary programming skills which I acquired not long ago are very much rusty these days. I was practicing with the code below but I received those two errors about the red line in the source code. Would you please help me?

I remember when I started posting here people would tell me that my code isn't properly organized, like braces are not aligned etc. They used to use a certain term. What is it? Please tell me. Thank you for the help.

//define_pi.cpp

// learning to use #define on Pi


#include <iostream>

#include <cstdlib>

#include <cmath>


using namespace std;


int main()

{

    float r, area;

    #define pi = 3.142;


    cout << "enter radius"; cin >> r;


    [B][COLOR="#FF0000"]area = 2*pi*r;[/COLOR][/B]


    cout << "area is: " << area << endl;


    system("pause");

    return 0;

}

Errors:

17|error: expected primary-expression before '=' token|

17|error: invalid type argument of 'unary *'|

[AKMafia001]

Well the term might be indentation. White Spaces are used to make your program more clear and readable.

---------- Post added at 12:16 AM ---------- Previous post was at 12:12 AM ----------

Put the #define directive in the begining of your progam.
One thing more i want to mention out is.

    #define pi = 3.142;

This isn't the way of writing #define directives. The correct form is,

    #define pi 3.142

[Flying Dutchman]

Note that macros are evil though.

[Alexander]

In C there are numerous places where #defines are your only option, for example (ignoring variable length arrays in C99), array[LEN] where LEN is a #define and not a constant. As well case statements,

const int foo = 2;
switch(...) {
  case foo:

Will not work, however if foo were a #define it would.

In C++ however, you can use constants in these places and the #define will cause unnecessary issues (it is replaced at compile time, it is not an actual variable in run time)

Unless you have a very good reason, you should be doing this, even at the global scope:

const float pi = 3.1415;

[jackson6612]

Thank you, AK, Dutchman, Alexander.