string  SpaceRemoval(string & EquationText)
{
    string NewEquationText = "";

    // check every character
    for (int i = 0; i < EquationText.length(); i++)
    {
        if (EquationText[i] != ' ') // if the character is not a ' ' then add it to the NewEquationText
        {
            NewEquationText += EquationText[i];
        }
    }

    // return the NewEquationText
    return NewEquationText;
}

second part
bool GetEquation()
{
    // Input equation
    cout << "Equation F(x) = ";
    cin >> EquationText;

    // Add Parentheses in the equation
    AddParentheses(EquationText);

    // Remove extra spaces in the equation
    EquationText = SpaceRemoval(EquationText);

    // Check if the equation is valid
    return EquationValidation(EquationText);
}

final part
#include "Header.h"

int main()
{

 while(true)
 {
    // Get Equation
    if (GetEquation())
    {
        // it's a valid equation
        calculateExpression(EquationText)
    }
    else
    {
        // it's a invalid equation
        cout << "invalid equationnn";
    }
 }