How can you change signs of the elements of Array in C++ - c++

Question

I just want to ask a question.
I am coding a system of linear equations in two variables using the 2-dimensional array. on the second equation, it is always multiplied with - so that it is easier to solve the x or y in equation 1.
how can you change the sign of the numbers in equation 2 if the ax+by= c is not the same?
I only know how to negate all the numbers in the second equation with the use of negative absolute value but I am facing difficulty if the user inputs on negative and positive numbers in equation 2.(-2x + 3y = -4).
Here is my code (it is not done since I am confused on how to change signs of an array independently because of the user input. I am just a beginner)
/*
Linear equation using elimination method
*/
#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
const int row = 2;
const int col = 3;
int list[row][col];
int list1[row][col];
int list2[row][col];
int rsize, y, x;
char operation;
int ir, ic;
int *ptr;
//function declaration
void equation1(int list[][col], int rsize);
//to display the value in 2D array plus linear equation
void Elimination(int list1[][col], int rsize);
//input the 2 values to elimate in eqn1 and eqn2
//then display the new equations that is already multiplied to the 2values
void final1(int list1[][col], int rsize,int Y);
//diplay the value of computed Y and the equation need to substitute the value of Y
//process and computes the value of X
//and finally, display the solution set of (x,y)
void final2(int list1[][col], int rsize,int X);
//diplay the value of computed X and the equation need to substitute the value of X
//process and computes the value of Y
//and finally, display the solution set of (x,y)
int deterY(int list2[3]); //computes the value of Y and returns the value of Y
int deterX(int list2[3]); //computes the value of X and returns the value of X
char choice(); //display the menu and returns the value of choice
int main() {
char opt, ulit, operation;
int equation;
opt = choice();
int solve_for_x, solve_for_y;
switch(opt) {
case '1': //two dimensional
do {
system("cls");
cout << "SYSTEMS OF LINEAR EQUATIONS:\n"
<< "Solving by addition or elimination\n";
//ADD CODE HERE
cout << "This program uses Addition or Elimination Method.\n"
<< "We begin by setting up and evaluating the three variables x, y and the constant.\n"
<< "For example,\n 5x + y = -14 \nshould be entered as 5 1 -14";
cout << "\n\nPress any key to continue....";
cin >> opt;
cin.ignore();
cin.get();
system("cls");
cout << "Again, 5x + y = -14 should be entered as 5 1 -14\n";
//ADD CODE HERE
equation1(list, row);
cin.ignore();
cout<<"\n\nPress any key to continue...." <<endl;
cin.get();
system("cls");
Elimination(list1, row);
cout << "\n\n\n";
cout << "What variable do you want to change: \n";
cout << "x or y\n";
cin >> operation;
switch(operation){
case 'x':
solve_for_x = deterX(list2[3]);
cout << solve_for_x <<endl;
break;
case 'y':
solve_for_y = deterY(list2[3]);
cout << solve_for_y << endl;
break;
}
//Call function Elimination here
//ADD CODE HERE
} while (toupper(ulit) == 'Y');
break;
case '2':
//ADD CODE HERE
break;
} //end switch
system("pause");
return 0;
} //end main
///////////////////////////////////////////////////////////
char choice() {
cout << "<<<<<<<MENU>>>>>>>" << endl;
cout <<"[1] Systems of Linear Equation"<<endl;
cout <<"[2] Quit" << endl;
cout <<"Enter your choice:" << endl;
char opt;
cin >> opt;
return opt;
}
///////////////////////////////////////////////////////////////
void equation1(int ist[][col], int rsize) {
cout << "Enter Equation 1:";
for(ir = 0; ir < row; ir++) {
for(ic = 0; ic < col; ic++) {
if(ir == 0 && ic >= 0) {
cin >> list[ir][ic];
}
if(ir == 1 && ic >= 0) {
cout << "Enter Equation 2:";
cin >> list[ir][ic];
}
}
}
} //end equation1
///////////////////////////////////////////////////////////
void Elimination(int list1[][col], int rsize) {
cout << "you have entered (using 2-dimensional array)" << endl;
for(ir = 0; ir < row; ir++) {
for(ic = 0; ic < col; ic++) {
cout < <setw(7) << list[ir][ic];
}
cout << endl;
}
cout << endl;
cout << "SOLVING SIMPLE EQUATIONS" << endl;
cout << setw(7) << list[0][0] << "x" << " + " <<list[0][1] << "y" << " = " << list[0][2] << endl;
cout << setw(7) << list[1][0] << "x" << " + " <<list[1][1] << "y" << " = " << list[1][2] << endl;
cout << "\n\n\n\n";
cout <<"_____________________________________________________ "<< endl;
cout << "Please enter the value to eliminate the variable" << endl;
cout << "for example... if you have:" <<endl;
cout << "2x + 3y = 10" << endl;
cout << "4x + 5y = 15" << endl;
cout << "if you want to eliminate the x.. you need to input -2" << endl;
cout << "(for 2x to become -4x in eqn.1) and 1 (to remain the value in eqn.2" << endl;
cout << "if you want to eliminate y.. you need to input -/+5 in eqn1 and +-3 in eqn.2" << endl;
cout << "enter the value for equation 1: 1 " << endl;
cout << "enter value for equation 2: -1 " << endl;
cout << "\n\n\n";
cout << "ELIMINATING EQUATIONS" << endl;
cout << setw(7) << list[0][0] <<"x" << " + " <<list[0][1] <<"y" << " = " << list[0][2] << endl;
cout << setw(7) << -abs(list[1][0])<<"x" << " + " << -abs(list[1][1]) <<"y" << " = " << -abs(list[1][2]) << endl;
cout <<"===================================================== "<< endl;
}
////////////////////////////////////////////////////
int deterY(int list2[3]){}
///////////////////////////////////////////////
int deterX(int list2[3]) {}
///////////////////////////////////////////////////////
void final1(int list1[][col], int rsize,int Y) {}
////////////////////////////////////////////////////////////////////////////
void final2(int list1[][col], int rsize,int X) {}