Why do I get these warnings in GCC 3.3 and yet compiles fine on vs.net.:Resolved:.

[voidflux]

GCC 3.3 compiler in a unix environment I get these warnings

homework5.cpp: In function `void isMagic(int*, int (*)[4], int, int)':
homework5.cpp:123: warning: ISO C++ forbids declaration of `magicCounter' with 
   no type
homework5.cpp:179: warning: name lookup of `row' changed for new ISO `for' 
   scoping
homework5.cpp:135: warning:   using obsolete binding at `row'

The reason i'm upset, is because my programming teacher is giving me a 55/100 on this homework assignment because he says, it doesn't compile. Thats bull**** because I just tested it and I just get warnings, not errors. I just need somthing to say to him to show him that, no i'm right, he's wrong, i shouldn't have got 55% on this homework becuase I get 3 warnings on a GCC compiler, and no warnings in .net. He also said, you can use any compiler you want as long as it uses the standard. Here's the program:

//File: homework5.cpp
//Written By: Cory Sanchez
/*Purpose:
The  generatEntries function creates 
a one-dimensional array of n2 elements 
ordered as the terms of an arithmetic 
sequence. The function also outputs the arithmetic 
sequence.
The program will then put the one-dimensional matrix
into a two-dimensional matrix and reverse the diagnoals.
A "magic number" is then generated, the program will then
compare the magic number with the sum of each row and column
if they are equal, the matrix has a "magic number".
*/

#include <iostream>
using namespace std;


void generateEntries(int matrix[], int size);
void createMatrix(int matrix[], int newMatrix[][4], int );
void reverseDiagonals(int newMatrix[][4], int row);
void printMatrix(int newMatrix[][4],int size);
void printMatrix(int matrix[], int size);
void isMagic(int matrix[], int newMatrix[][4], int size1, int size2);

int main()
{
	const int ROW = 4;
	const int COL = 4;
	int SIZE = 16;						//number of rows * columns == size of whole matrix

	int matrix[ROW*COL];
	int newMatrix[ROW][COL];
	generateEntries(matrix,SIZE);
	createMatrix(matrix,newMatrix,ROW);
	printMatrix(newMatrix,ROW);
	reverseDiagonals(newMatrix,ROW);
	printMatrix(newMatrix,ROW);
	isMagic(matrix,newMatrix,SIZE,ROW);
	return 0;
}

void generateEntries(int matrix[], int size)
{
	int first, difference;
	cout <<"Enter two numbers: ";
	cin >> first >> difference;
	
	matrix[0] = first;
	for(int i = 1; i < size; i++)
	{
		matrix[i] = difference+matrix[i-1];
	}

	printMatrix(matrix,size);
	
}

void createMatrix(int matrix[], int newMatrix[][4], int row)
{
	static int counter = 0;		//to iterate through a of matrix[i]
	for(int i = 0; i < row; i++)
	{
		for(int j = 0; j < row; j++, counter++)
		{
			newMatrix[i][j] = matrix[counter];
		}
	}
}

void reverseDiagonals(int newMatrix[][4], int row)
{
	int temp;

	for(int i = 0; i < row/2; i++)
	{
		temp = newMatrix[i][i];
		newMatrix[i][i] = newMatrix[row-1-i][row-1-i];
		newMatrix[row-1-i][row-1-i] = temp;
	}
	for(int j = 0; j < row/2; j++)
	{
		temp = newMatrix[j][row-1-j];
		newMatrix[j][row-1-j] = newMatrix[row-1-j][j];
		newMatrix[row-1-j][j] = temp;
	}
}

void printMatrix(int newMatrix[][4],int size)
{
	for(int i = 0; i < size; i++)
		{
		for(int j = 0; j < size; j++)
			{
			if(j%4 == 0)
				{
				cout << endl;
				}
				cout << newMatrix[i][j]<<" ";
			}
		}
		cout << endl;
}

void printMatrix(int matrix[], int size)
{
	for(int i =0; i < size; i++)
	{
		cout <<matrix[i]<<" ";
	}
	cout << endl;
}

void isMagic(int matrix[], int newMatrix[][4], int size1, int size2)
{
	int sum = 0;				//holds the sum of the 1-dim array
	int colSum = 0;
	int rowSum = 0;
	int mainDSum = 0;
	int oppDSum = 0;
	int magicNum = 0;
	static magicCounter = 0;	//keeps track of the magic rows/columns
	
	//generating the magic number
	for(int i = 0; i < size1; i++)
	{
		sum += matrix[i];
	}
	
	magicNum = sum/size2;			//sum divided by # of rows
	
	cout <<"magic number: " << magicNum << endl;
	//adding up rows
	for(int row = 0; row < size2; row++)
	{
		rowSum = 0;
		for(int col = 0; col < size2; col++)
		{
			rowSum = rowSum + newMatrix[row][col];
		}
		
		if(rowSum == magicNum)			
		{
			magicCounter++;
		}
	}
	
	//adding up cols
	for(int col = 0; col < size2; col++)
	{
		colSum = 0;
		for(int row = 0; row < size2; row++)
		{
			colSum = colSum + newMatrix[row][col];
		}
		
		if(colSum == magicNum)
		{
			magicCounter++;
		}
	}

	//add up main diagnoal
	for(int i = 0; i < size2/2; i++)
	{
		mainDSum = mainDSum + newMatrix[i][i];
		mainDSum += newMatrix[size2-1-i][size2-1-i];
	}
	if(mainDSum == magicNum)
	{
		magicCounter++;
	}

	//add up opposite diagnoal
	for(int i = 0; i < size2/2; i++)
	{
		oppDSum += newMatrix[i][size2-1-i];
		oppDSum += newMatrix[row-1-i][i];
	}
	if(oppDSum == magicNum)
	{
		magicCounter++;
	}
	
	//check if matrix has a magic number
	if(magicCounter == (2 * size2+2))
	{
		cout <<"This matrix has a magic number!\n";
	}
	else
	{
		cout <<"This matrix has no magic number!\n";
	}
	
}

[Technocrat]

He must be smoking crack because it just compiled for me with 0 errors or warnings on .NET 2003. Looks good to me execept the static delecration. So I see no reason to 1/2 your grade.

[Comreak]

Have you tried telling him that it compiles fine under VS.NET (which is still pretty standard compliant)? In the future, the best thing to do would be do download GCC and test your programs to make sure they work. This way, you can catch all the little errors you might get in class before they happen.

Good luck convincing your professor.

[voidflux]

alright thanks guys, i'll tell you how it goes tomarrow afternoon

[twanvl]

The warnings the compiler gives you are correct,

static magicCounter = 0;

This variable doesn't have a type (static is not a type, it is a storage-class specifier) you need to declare the variable as

static int magicCounter = 0;

But you probably didn't mean for it to be static. Static here means that the value of the variable will be preserved with repeated calls to the same function.

oppDSum += newMatrix[row-1-i][i];

You are using the variable row outside the scope it is declared in. In C++ variables declared in for loops exist only in the loops scope (VS 6 disagrees, don't know about .net)

[voidflux]

I thought in .net if you write static variable name, it assumes the type is integer.

[parksie]

Assuming a type is int is a hold-off from older C. Implicit int is removed in later versions of the C standard.

[voidflux]

ahhh, I feel much better, now my grade changed from a 55/100, to a 100/100! He shouldn't have said, "we can use microsoft compiler", he doesn't talk english well. Another odd thing I found out about GCC, when you overload an operator such as + or -, it will throw up errors all over the place if you try a statement like this:

assume p1 and p2 are objects of class polynomial
cout <<p1<<"+"<<p2 <<"="<< p1+p2 <<endl;
to fix that problem you have to do this which just seems like more code to me:
polynomial x = p1+p2;
cout <<p1<<"+"<<p2 <<"="<< x <<endl;

[CornedBee]

Have you tried
cout <<p1<<"+"<<p2 <<"="<< (p1+p2) <<endl;
?

But actually your teacher is correct. I don't think VC++ would compile your code with the /Za (ANSI enforcement) switch, neither would GCC with a similar switch (-ansi I think). The first two warnings would be errors then.

[voidflux]

Why would you not allow,

cout << p1+p2<<endl;

whats so dangerous about this code?

[parksie]

Perhaps operator+ isn't defined correctly.

[CornedBee]

Bitshift has lower precedence than +, so actually it should work. But who knows...

I always use parentheses on things between cout's <<.


What errors does it give you anyway?
And what's the declaration and implementation of operator + of polynomial?

[voidflux]

I don't get any errors on .net environment, its when I use GCC 3.1 I get tons of errrors, here's the class definition and declaration of the overloaded +/- operators and the << operators
assume class Polynomial, which has 2 data members, int a, b, c;

Polynomial operator+ (const Polynomial& p1);
Polynomial operator- (const Polynomial& p1);
friend ostream &operator<<(ostream &out, Polynomial& p1);


ostream &operator<<(ostream &out, Polynomial &p1)
{
	if(p1.b >0 && p1.c>=0)
	{
		out <<p1.a<<"x^2+"<<p1.b<<"x+"<<p1.c;
	}
	else if(p1.b<0 && p1.c<0)
	{
		out <<p1.a<<"x^2"<<p1.b<<"x"<<p1.c;
	}
	else if(p1.b<0 && p1.c>=0)
	{
		out <<p1.a<<"x^2"<<p1.b<<"x+"<<p1.c;
	}
	else 
	{
		out <<p1.a<<"x^2+"<<p1.b<<"x"<<p1.c;
	}
	return out;
}

Polynomial Polynomial::operator+ (const Polynomial& p1)
{
	Polynomial p3;		//holds the new value of calling object + another object
	p3.a = a + p1.a;
	p3.b = b + p1.b;
	p3.c = c + p1.c;
	return p3;
}

Polynomial Polynomial::operator- (const Polynomial& p1)
{
	Polynomial p3;
	p3.a = a - p1.a;
	p3.b = b - p1.b;
	p3.c = c - p1.c;
	return p3;
}

Here's just a tad of the errors I get:

test.cpp: In member function `double Polynomial::getBiggerRoot()':
test.cpp:52: error: call of overloaded `sqrt(int)' is ambiguous
/usr/include/architecture/ppc/math.h:249: error: candidates are: double 
   sqrt(double)
/usr/include/gcc/darwin/3.3/c++/cmath:465: error:                 long double 
   std::sqrt(long double)
/usr/include/gcc/darwin/3.3/c++/cmath:461: error:                 float 
   std::sqrt(float)
test.cpp: In member function `double Polynomial::getSmallerRoot()':
test.cpp:73: error: call of overloaded `sqrt(int)' is ambiguous
/usr/include/architecture/ppc/math.h:249: error: candidates are: double 
   sqrt(double)
/usr/include/gcc/darwin/3.3/c++/cmath:465: error:                 long double 
   std::sqrt(long double)
/usr/include/gcc/darwin/3.3/c++/cmath:461: error:                 float 
   std::sqrt(float)
test.cpp: In function `int main()':
test.cpp:257: error: no match for `std::basic_ostream<char, 
   std::char_traits<char> >& << Polynomial' operator
/usr/include/gcc/darwin/3.3/c++/bits/ostream.tcc:63: error: candidates are: 
   std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, 
   _Traits>::operator<<(std::basic_ostream<_CharT, 
   _Traits>&(*)(std::basic_ostream<_CharT, _Traits>&)) [with _CharT = char, 
   _Traits = std::char_traits<char>]
/usr/include/gcc/darwin/3.3/c++/bits/ostream.tcc:85: error:                 
   std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, 
   _Traits>::operator<<(std::basic_ios<_CharT, 
   _Traits>&(*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits 
   = std::char_traits<char>]
/usr/include/gcc/darwin/3.3/c++/bits/ostream.tcc:107: error:                 
   std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, 
   _Traits>::operator<<(std::ios_base&(*)(std::ios_base&)) [with _CharT = char, 
   _Traits = std::char_traits<char>]
/usr/include/gcc/darwin/3.3/c++/bits/ostream.tcc:179: error:                 
   std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, 
   _Traits>::operator<<(long int) [with _CharT = char, _Traits = 
   std::char_traits<char>]

The errrors go on for about 5 pages!

[twanvl]

The first few errors are about the sqrt function. You are applying it to ints, but the compiler is unsure whether to use the double or the float version of sqrt. An explicit static_cast<float>(some_int_value) would fix this error.
The other errors are caused by your operator <<. It takes a Polynomial&, but according to the standard you can't take a reference to a temporary object. The values returned by operator + are temporary. A solution would be to let the operator << take a const Polynomial&

[voidflux]

excellent! thanks for clearing that up!