operator overloading - C++ error: passing xxx as 'this' argument of xxx discards qualifiers -

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• discards qualifiers error 4 answers

this code i've written access matrix in class , compare 2 objects of same class using less operator , equal operator. compiler throws errors.

#include <bits/stdc++.h> using namespace std;  class node { private:   int a[5][5];  public:   int& operator()(int i, int j) {     return a[i][j];   }    friend bool operator==(const node& one, const node& two);   friend bool operator<(const node& one, const node& two); };  bool operator==(const node& one, const node& two) {   (int = 1; < 5; i++) {     (int j = 1; j < 5; j++) {       if (one(i, j) != two(i, j)) {         return false;       }     }   }   return true; }  bool operator<(const node& one, const node& two) {   (int = 1; < 5; i++) {     (int j = 1; j < 5; j++) {       if (one(i, j) > two(i, j)) {         return false;       }     }   }   return true; }  int main() {   node src;   (int = 1; < 5; i++) {     (int j = 1; j < 5; j++) {       cin >> src(i, j);     }   }   return 0; } 

the compile time error is:

code.cpp: in function 'bool operator==(const node&, const node&)': code.cpp:20:19: error: passing 'const node' 'this' argument of 'int& node::operator()(int, int)' discards qualifiers [-fpermissive]        if (one(i, j) != two(i, j)) {                    ^ code.cpp:20:32: error: passing 'const node' 'this' argument of 'int& node::operator()(int, int)' discards qualifiers [-fpermissive]        if (one(i, j) != two(i, j)) {                                 ^ code.cpp: in function 'bool operator<(const node&, const node&)': code.cpp:31:19: error: passing 'const node' 'this' argument of 'int& node::operator()(int, int)' discards qualifiers [-fpermissive]        if (one(i, j) > two(i, j)) {                    ^ code.cpp:31:31: error: passing 'const node' 'this' argument of 'int& node::operator()(int, int)' discards qualifiers [-fpermissive]        if (one(i, j) > two(i, j)) { 

can tell me going wrong?

add

const int operator()(int i, int j) const {   return a[i][j]; }