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Feedback on beginner math program

Obsidian (1)
If this is the proper place to ask for feedback on the efficiency of code, then here is a short program I wrote today. I just started C++ today, and have no other
experience with coding.

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#include <iostream>
#include <math.h>
using namespace std;

int main() {
    
    string n,answers;
    double a,b;
    double c,d;
    int i,is_prime;
    
    label1:
    cout << "Input a number.\n";
    cin >> a;
    cout << "The square of " << a << " is " << a*a << ".\n";
    cout << "The cube of " << a << " is " << a*a*a << ".\n";
    
    if ((int)a % 2 == 0)
       cout << a << " is an even number.\n";
    else
        cout << a << " is an odd number.\n";
    
    i = 2;
    while (i <= sqrt(static_cast<double>(a))) {
          if ((int)a % i == 0)
          is_prime = false;
          i++;
          }
    
    if (is_prime)
       cout << a << " is a prime number.\n";
    else
        cout << a << " is not a prime number.\n";
    
    cout << "Would you like to continue? (y/n): ";
    cin >> n;
    if (n == "y")
       goto labelcont;
    if (n == "yes")
       goto labelcont;
    if (n == "n")
       goto labelend;
    if (n== "no")
       goto labelend;    
    else 
         cout << "Improper syntax, closing... \n";
         goto labelend;
         
    labelcont:
    cout << "What would you like to do? (+,-,*,/,restart,end): ";
    cin >> answers;
    
    if (answers == "+")
       goto label_plus;
    if (answers == "-")
       goto label_minus;
    if (answers == "*")
       goto label_mult;
    if (answers == "/")
       goto label_div;
    if (answers == "r")
       goto label1;
    if (answers == "restart")
       goto label1;
    if (answers == "e")
       goto labelend;
    if (answers == "end")
       goto labelend;
    else cout << "Incorrect syntax. Closing...";
    goto labelend;
    
    label_plus:
    cout << "Enter a number to start with: ";
    cin >> a;
    cout << "\nEnter a number to add to " << a << ": ";
    cin >> b;
    cout << "\n" << a << " + " << b << " = " << a+b << "\n\n";
    goto labelcont;
    
    label_minus:
    cout << "Enter the first number: ";
    cin >> a;
    cout << "\nEnter the second number: ";
    cin >> b;
    cout << "\n" << a << " - " << b << " = " << abs((int)a-(int)b) << "\n\n";
    goto labelcont;
    
    label_mult:
    cout << "Enter the first number: ";
    cin >> a;
    cout << "\nEnter the number to multiply by " << a << ": ";
    cin >> b;
    cout << "\n" << a << " * " << b << " = " << a*b << "\n\n";    
    goto labelcont;
    
    label_div:
    cout << "Enter the first number: ";
    cin >> a;
    cout << "\nEnter the second number: ";
    cin >> b;
    cout << "\n" << a << " / " << b << " = " << a/b << "\n\n";
    goto labelcont;
    
    labelend:
    return 0;
}


I would just like some feedback on the code, preferably methods on how I can optimize it. I have noticed a lot of people hate 'goto', but I could not think of another way to have the program go back to the start without it.
metulburr (585)
all the goto's can be replaced if you restructure your program using functions, and loops.
ar2007 (210)

in your code,can delete the goto statement if you use switch instead of if / else, with the addition of functions.
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