CODEWITHSUNDEEP
c++c-preprocessor
SoajanII
SoajanII

Reputation: 441

#define and invalid type argument of unary ‘*’ (have ‘double’)

Just started programming C++, and stuck on the code below. On Ubuntu terminal I try to compile with

g++ -o circleArea circleArea.cpp

I get the error:

circleArea.cpp: In function ‘int main()’:
circleArea.cpp:14:14: error: invalid type argument of unary ‘*’ (have ‘double’)
  area = PI * r * r;
              ^

The code is :

#include <iostream>

using namespace std;

#define PI 3.14159;
#define newLine "\n";

int main(void)
{
    double r;
    double area;
    cout << "Please enter the radius : ";
    cin >> r;
    area = PI * r * r;
    cout << "Area is " << area << " unit squares" << newLine;   
}

If replace the line "area = PI * r * r" with "area = 3.14159 * r * r" I don't get any errors. What is the problem, can you help?

Thank you

Upvotes: 1

Views: 5428

Answers (1)

timrau
timrau

Reputation: 23058

With #define PI 3.14159;,

area = PI * r * r;

becomes

area = 3.14159; * r * r;

Note the extra ; between 3.14159 and * r. It's like

area = 3.14159;
* r * r;

and thus the first * is treated as a unary dereference operator. You should remove the semicolon in the end of macro definition.

Upvotes: 8

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