Compilare: main.cpp: In member function 'const Matrix Matrix::operator+(Matrix)': main.cpp:81:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < rows; i++) { ~~^~~~~~ main.cpp:82:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < columns; j++) { ~~^~~~~~~~~ main.cpp: In member function 'const Matrix Matrix::operator-(Matrix)': main.cpp:93:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < rows; i++) { ~~^~~~~~ main.cpp:94:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < columns; j++) { ~~^~~~~~~~~ main.cpp: In member function 'const Matrix Matrix::operator*(Matrix)': main.cpp:114:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = 0; k < columns; k++) { ~~^~~~~~~~~ main.cpp: In member function 'const Matrix Matrix::multiply_with_modulo(Matrix, int)': main.cpp:135:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = 0; k < columns; k++) { ~~^~~~~~~~~