Good morning. I been dealing with this error for 3 days now and I

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Asked: May 21, 20262026-05-21T09:38:43+00:00 2026-05-21T09:38:43+00:00

Good morning. I been dealing with this error for 3 days now and I

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Good morning. I been dealing with this error for 3 days now and I can’t figure it out. I was tasked to create a header file for a series of matrix tests to learn the use of of templates on c++. I seem to have all other operators working except for operator*=. I am including the header file, plus the error I am getting.

#ifndef MATRIX_H
#define MATRIX_H
#include <vector>
#include <iostream>
#include <math.h>
#include <complex>

using namespace std;
namespace nkumath {

template <typename T, size_t ROWS, size_t COLS>
class Matrix {
    friend class Matrix;
public:

    Matrix(const T & init = T()) : elts(ROWS, vector<T>(COLS, init)) {
    };

    const vector<T> & operator[](int ROWS) const {
        return elts[ROWS];
    }; //not sure if correct

    vector<T> & operator[](int ROWS) {
        return elts[ROWS];
    }; //not sure if correct

    //MatrixAdd
    Matrix & matrixAdd(const Matrix & lhs, const Matrix & rhs) {
        for (int r = 0; r < ROWS; r++) {
            for (int c = 0; c < COLS; c++) {
                this->elts[r][c] = lhs[r][c] + rhs[r][c];
            }
        }
        return *this;
    };

    //MatrixSubtract

    Matrix & matrixSubtract(const Matrix & lhs, const Matrix & rhs) {

        for (int r = 0; r < ROWS; r++) {
            for (int c = 0; c < COLS; c++) {
                this->elts[r][c] = lhs[r][c] - rhs[r][c];
            }
        }
        return *this;
    };

    //MatrixMult

    template<size_t INNER>
    Matrix & matrixMult(const Matrix<T, ROWS, INNER> & mat1, const Matrix<T, INNER, COLS> & mat2) {
        for (int i = 0; i < ROWS; i++) {
            for (int j = 0; j < COLS; j++) {
                //elts[i][j] = 0;
                for (int k = 0; k < INNER; k++) {
                    elts[i][j] += mat1.elts[i][k] * mat2.elts[k][j];
                }
            }
        }
        return *this;
    }; //not done

    //print function

    void print(ostream & out) const {
        for (int i = 0; i < ROWS; i++) {
            for (int j = 0; j < COLS; j++) {
                out << elts[i][j];
            }
            out << "\n";
        }
    };

private:
    vector< vector<T> > elts;
};
//Note, you have to define each time a template to avoid having the errors
//Operator<<

template <typename T, size_t ROWS, size_t COLS>
ostream & operator<<(ostream & out, const Matrix<T, ROWS, COLS> & elts) {
    elts.print(out);
    return out;
};

//Operator==

template <typename T, size_t ROWS, size_t COLS>
bool operator==(const Matrix<T, ROWS, COLS> & lhs, const Matrix<T, ROWS, COLS> & rhs) {
    return true;
};
//Operator+

template <typename T, size_t ROWS, size_t COLS>
Matrix<T, ROWS, COLS> operator+(const Matrix<T, ROWS, COLS> & lhs, const Matrix<T, ROWS, COLS> & rhs) {
    Matrix<T, ROWS, COLS> returnVal;
    return returnVal.matrixAdd(lhs, rhs);
};
//Operator-

template <typename T, size_t ROWS, size_t COLS>
Matrix<T, ROWS, COLS> operator-(const Matrix<T, ROWS, COLS> & lhs, const Matrix<T, ROWS, COLS> & rhs) {
    Matrix<T, ROWS, COLS> returnVal;
    return returnVal.matrixSubtract(lhs, rhs);
};
//Operator*

template <typename T, size_t ROWS, size_t COLS>
Matrix<T, ROWS, COLS> operator*(const Matrix<T, ROWS, COLS> & lhs, const Matrix<T, ROWS, COLS> & rhs) {
    Matrix<T, ROWS, COLS> returnVal;
    return returnVal.matrixMult(lhs, rhs);
};

//Operator+=

template <typename T, size_t ROWS, size_t COLS, typename C>
Matrix<T, ROWS, COLS> operator+=(Matrix<T, ROWS, COLS> & lhs, const C & rhs) {
    //Matrix<T,ROWS,COLS> returnVal;
    lhs.matrixAdd(lhs, rhs);
    return lhs;
};

//Operator-=

template <typename T, size_t ROWS, size_t COLS, typename C>
Matrix<T, ROWS, COLS> operator-=(Matrix<T, ROWS, COLS> & lhs, const C & rhs) {
    lhs.matrixSubtract(lhs, rhs);
    return lhs;
};
//Operator*=

template <typename T, size_t ROWS, size_t COLS, typename C>
Matrix<T, ROWS, COLS> operator*=(Matrix<T, ROWS, COLS> & lhs, const C & rhs) {
    lhs.matrixMult(lhs, rhs);
    return lhs;
};
//Operator/=

template <typename T, size_t ROWS, size_t COLS>
Matrix<T, ROWS, COLS> operator/=(const Matrix<T, ROWS, COLS> & lhs, const int rhs) {
    Matrix<T, ROWS, COLS> returnVal(rhs);
    for (int r = 0; r < ROWS; r++) {
        for (int c = 0; c < COLS; c++) {
            returnVal[r][c] = lhs[r][c] / returnVal[r][c];
        }
    }
    return returnVal;
};
//Operator%=

template <typename T, size_t ROWS, size_t COLS>
Matrix<T, ROWS, COLS> operator%=(const Matrix<T, ROWS, COLS> & lhs, const int rhs) {
    Matrix<T, ROWS, COLS> returnVal(rhs);
    for (int r = 0; r < ROWS; r++) {
        for (int c = 0; c < COLS; c++) {
            returnVal[r][c] = lhs[r][c] % returnVal[r][c];
        }
    }
    return returnVal;
};
    } // namespace Matrix

    #endif // MATRIX_H

here is my main.cpp. I am not allowed to change this file….

// main.cpp
// Test driver for Matrix class template project.
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>  // for rand()
#include "Matrix.h"

using namespace std;
using namespace nkumath;

template <typename T, size_t ROWS, size_t COLS>
void randomize(Matrix<T, ROWS, COLS> & mat)
// Put random values in a Matrix.
// Note:  It must be possible to assign T an int value.
{
for (size_t i = 0; i < ROWS; i++)
    for (size_t j = 0; j < COLS; j++)
        mat[i][j] = (rand() % 21) - 10; // Random number in range -10,...,+10
}

struct Complex
{
Complex(double re = 0.0, double im = 0.0) : real(re), imag(im) { }
Complex & operator+=(const Complex & rhs)
{
    real += rhs.real;
    imag += rhs.imag;
    return *this;
}
Complex & operator-=(const Complex & rhs)
{
    real -= rhs.real;
    imag -= rhs.imag;
    return *this;
}
Complex & operator*=(const Complex & rhs)
{
    real = real * rhs.real - imag * rhs.imag;
    imag = real * rhs.imag + imag * rhs.real;
    return *this;
}
double real;
double imag;
};
Complex operator+(const Complex & lhs, const Complex & rhs)
{
return Complex(lhs.real + rhs.real, lhs.imag + rhs.imag);
}
Complex operator-(const Complex & lhs, const Complex & rhs)
{
return Complex(lhs.real - rhs.real, lhs.imag - rhs.imag);
}
Complex operator*(const Complex & lhs, const Complex & rhs)
{
return Complex(lhs.real * rhs.real - lhs.imag * rhs.imag, lhs.real * rhs.imag + lhs.imag * rhs.real);
}
ostream & operator<<(ostream & out, const Complex & c)
{
out << "(" << c.real << " + " << c.imag << "i)";
return out;
}


int main()
{
srand(100);
ofstream out("output.txt");

// Matrix construction, operator[], and printing:
Matrix<int, 4, 5> m1(2);
out << "m1: " << endl;
m1.print(out);
const Matrix<int, 4, 5> m2 = m1;
out << "m2: " << endl << m2;
for (size_t i = 0; i < 4; i++)
    m1[i][i] = 5;
out << "m1: " << endl << m1;

// Tests of const correctness:
// m2[0][0] = 0; // This line should not compile.
// m2 += 4; // Neither should this one.
int n = m2[0][0]; // This line should be okay.

// Scalar operation tests:
out << "m1 += 4: "  << endl << (m1 += 4);
out << "m1 -= 6: " << endl << (m1 -= 6);
out << "m1 *= 12: " << endl << (m1 *= 12);
out << "m1 /= 2: " << endl << (m1 /= 2);
out << "m1 %= 7: " << endl << (m1 %= 7);

// Matrix addition and subtraction tests:
Matrix<int, 4, 5> m3;
out << "m3: " << endl << m3;
out << "m3.matrixAdd(m1, m2): " << endl << m3.matrixAdd(m1, m2);
out << "m3.matrixSubtract(m1, m2): " << endl << m3.matrixSubtract(m1, m2);
out << "m2 + m1: " << endl << (m2 + m1);
out << "m2 - m1: " << endl << (m2 - m1);

// Matrix multiplication tests:
Matrix<int, 2, 3> m4;
randomize(m4);
out << "m4: " << endl << m4;
Matrix<int, 3, 5> m5;
randomize(m5);
out << "m5: " << endl << m5;
Matrix<int, 2, 5> m6;
out << "m6.matrixMult(m4, m5): " << endl << m6.matrixMult(m4, m5);
Matrix<int, 2, 5> m7;
matrixMult(m4, m5, m7);
out << "m6 == m7: " << (m6 == m7) << endl;
out << "m6 == m4 * m5: " << (m6 == m4 * m5) << endl;

// Matrices of strings:
Matrix<string, 3, 4> m8("Hello");
for (size_t i = 0; i < 3; i++)
    m8[i][i] = "   Hi";
out << "m8: " << endl << m8 << endl;
Matrix<string, 3, 4> m9(" there!");
out << "m9: " << endl << m9 << endl;
out << "m8 + m9: " << endl << m8 + m9 << endl;
Matrix<string, 4, 5> m10(", Goodbye!");
//out << m8 * m10 << endl; // This line should not compile.

// Matrices of Complex:
Matrix<Complex, 2, 8> m11;
randomize(m11);
Complex c(1, -3);
m11 += c;
out << "m11: " << endl << m11 << endl;
Matrix<Complex, 8, 3> m12;
randomize(m12);
m12 -= c;
out << "m12: " << endl << m12 << endl;
out << "m11 * m12: " << endl << m11 * m12 << endl;

out.close();
}

The error I am getting is

Error   1   error C2784: 'nkumath::Matrix<T,ROWS,COLS> &nkumath::Matrix<T,ROWS,COLS>::matrixMult(const nkumath::Matrix<T,4,INNER> &,const nkumath::Matrix<T,INNER,5> &)' : could not deduce template argument for 'const nkumath::Matrix<T,INNER,5> &' from 'const int' e:\documents and settings\pato\my documents\visual studio 2010\projects\thematrix\thematrix\matrix.h    136

I am using visual studio c++ 2010. I tried to compile the header on linux gcc4 and I goth a whole different set of errors, so I am going to finish this project in windows. Either way just need someone to point me to the right direction, I have been looking at this for too long.
Thank you!
PJ

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1 Answer

Editorial Team · Answer 1 · 2026-05-21T09:38:43+00:00

In your main

you were missing the using namespace std and using namespace nkumath declarations
there is a call matrixMult(m4, m5, m7); which cannot resolve. I’m assuming you mean m7 = m4*m5;

It seems like you have incorrectly made a previously static matrixMult (with the meaning of innerproduct) into a member function of Matrix;

Using this as a freestanding static function works:

    template<class T, size_t ROWS, size_t INNER, size_t COLS>
    static Matrix<T, ROWS, COLS> innerProduct(const Matrix<T, ROWS, INNER> & mat1, const Matrix<T, INNER, COLS> & mat2) {
        Matrix<T, ROWS, COLS> result;
        for (int i = 0; i < ROWS; i++) {
            for (int j = 0; j < COLS; j++) {
                //elts[i][j] = 0;
                for (int k = 0; k < INNER; k++) {
                    result.elts[i][j] += mat1.elts[i][k] * mat2.elts[k][j];
                }
            }
        }
        return result;
    } //not done

Update

It means that you should rewrite the matrixMult method like so (using the above static innerProduct helper):

    template<size_t OUTER>
    Matrix<T, ROWS, OUTER> matrixMult(const Matrix<T, COLS, OUTER> & mat2) const {
        return innerProduct(*this , mat2);
    }

also adding something like this is probably what you want:

template<class T, size_t ROWS, size_t INNER, size_t COLS>
Matrix<T, ROWS, COLS> operator*(const Matrix<T, ROWS, INNER> & lhs, const Matrix<T, INNER, COLS> & rhs)
    {
        return innerProduct(lhs, rhs);
    }

I haven’t bothered fixing the scalar multiplication, but you should get the idea now (if I’m not wasting my time). Good luck

This way the main.cpp can stay as it was… capice?

This is my resulting Matrix class definition for your perusal:

namespace nkumath {

    template <typename T, size_t ROWS, size_t COLS>
    class Matrix {
    public:

        Matrix(const T & init = T()) : elts(ROWS, vector<T>(COLS, init)) {
        }

        const vector<T> & operator[](int r) const {
            return elts[r];
        } //not sure if correct

        vector<T> & operator[](int r) {
            return elts[r];
        } //not sure if correct

        //MatrixAdd
        Matrix & matrixAdd(const Matrix & lhs, const Matrix & rhs) {
            for (int r = 0; r < ROWS; r++) {
                for (int c = 0; c < COLS; c++) {
                    this->elts[r][c] = lhs[r][c] + rhs[r][c];
                }
            }
            return *this;
        }

        //MatrixSubtract

        Matrix & matrixSubtract(const Matrix & lhs, const Matrix & rhs) {

            for (int r = 0; r < ROWS; r++) {
                for (int c = 0; c < COLS; c++) {
                    this->elts[r][c] = lhs[r][c] - rhs[r][c];
                }
            }
            return *this;
        }

        //MatrixMult

        template<size_t OUTER>
        Matrix<T, ROWS, OUTER> matrixMult(const Matrix<T, COLS, OUTER> & mat2) const {
            return innerProduct(*this , mat2);
        } //not done

        //print function

        void print(ostream & out) const {
            for (int i = 0; i < ROWS; i++) {
                for (int j = 0; j < COLS; j++) {
                    out << elts[i][j];
                }
                out << "\n";
            }
        }

    private:
        vector< vector<T> > elts;
    };
    //Note, you have to define each time a template to avoid having the errors
    //Operator<<

        template<class T, size_t ROWS, size_t INNER, size_t COLS>
        static Matrix<T, ROWS, COLS> innerProduct(const Matrix<T, ROWS, INNER> & mat1, const Matrix<T, INNER, COLS> & mat2) {
            Matrix<T, ROWS, COLS> result;
            for (int i = 0; i < ROWS; i++) {
                for (int j = 0; j < COLS; j++) {
                    //elts[i][j] = 0;
                    for (int k = 0; k < INNER; k++) {
                        result.elts[i][j] += mat1.elts[i][k] * mat2.elts[k][j];
                    }
                }
            }
            return result;
        } //not done
    template <typename T, size_t ROWS, size_t COLS>
    ostream & operator<<(ostream & out, const Matrix<T, ROWS, COLS> & elts) {
        elts.print(out);
        return out;
    }

    //Operator==

    template <typename T, size_t ROWS, size_t COLS>
    bool operator==(const Matrix<T, ROWS, COLS> & lhs, const Matrix<T, ROWS, COLS> & rhs) {
        return true;
    }
    //Operator+

    template <typename T, size_t ROWS, size_t COLS>
    Matrix<T, ROWS, COLS> operator+(const Matrix<T, ROWS, COLS> & lhs, const Matrix<T, ROWS, COLS> & rhs) {
        Matrix<T, ROWS, COLS> returnVal;
        return returnVal.matrixAdd(lhs, rhs);
    }
    //Operator-

    template <typename T, size_t ROWS, size_t COLS>
    Matrix<T, ROWS, COLS> operator-(const Matrix<T, ROWS, COLS> & lhs, const Matrix<T, ROWS, COLS> & rhs) {
        Matrix<T, ROWS, COLS> returnVal;
        return returnVal.matrixSubtract(lhs, rhs);
    }
    //Operator*

    template <typename T, size_t ROWS, size_t COLS>
    Matrix<T, ROWS, COLS> operator*(const Matrix<T, ROWS, COLS> & lhs, const Matrix<T, ROWS, COLS> & rhs) {
        Matrix<T, ROWS, COLS> returnVal;
        return returnVal.matrixMult(lhs, rhs);
    }

    //Operator+=

    template <typename T, size_t ROWS, size_t COLS, typename C>
    Matrix<T, ROWS, COLS> operator+=(Matrix<T, ROWS, COLS> & lhs, const C & rhs) {
        //Matrix<T,ROWS,COLS> returnVal;
        lhs.matrixAdd(lhs, rhs);
        return lhs;
    }

    //Operator-=

    template <typename T, size_t ROWS, size_t COLS, typename C>
    Matrix<T, ROWS, COLS> operator-=(Matrix<T, ROWS, COLS> & lhs, const C & rhs) {
        lhs.matrixSubtract(lhs, rhs);
        return lhs;
    }
    //Operator*=

    template <typename T, size_t ROWS, size_t COLS, typename C>
    Matrix<T, ROWS, COLS> operator*=(Matrix<T, ROWS, COLS> & lhs, const C & rhs) {
        lhs.matrixMult(lhs, rhs);
        return lhs;
    }
    //Operator/=

    template <typename T, size_t ROWS, size_t COLS>
    Matrix<T, ROWS, COLS> operator/=(const Matrix<T, ROWS, COLS> & lhs, const int rhs) {
        Matrix<T, ROWS, COLS> returnVal(rhs);
        for (int r = 0; r < ROWS; r++) {
            for (int c = 0; c < COLS; c++) {
                returnVal[r][c] = lhs[r][c] / returnVal[r][c];
            }
        }
        return returnVal;
    }
    //Operator%=

    template <typename T, size_t ROWS, size_t COLS>
    Matrix<T, ROWS, COLS> operator%=(const Matrix<T, ROWS, COLS> & lhs, const int rhs) {
        Matrix<T, ROWS, COLS> returnVal(rhs);
        for (int r = 0; r < ROWS; r++) {
            for (int c = 0; c < COLS; c++) {
                returnVal[r][c] = lhs[r][c] % returnVal[r][c];
            }
        }
        return returnVal;
    }
}

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Good morning. I been dealing with this error for 3 days now and I

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