[HELP]Help with C++ error?

Hi I was recently coding a prime # finder, calculator, sum/product function, and quadratic equation solver for my class and something really weird happens. I compile and it works fine, but when I run and type 3 for calculator it goes to if(choice = 1){...} instead of if(choice = 3){...}. But then it also runs the if(choice=3{...}. Can any1 help me?
Here is code

Wrong:
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if(choice = 3) {...}
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Right:
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if(choice == 3){...}
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You need 2 "=" signs, Or it will screw up.

And this counts for the 2 other "if"'s as well

It works fine for me..

Right after 'top:' you put choice = 2; for some reason.. remove it.


Code that worked for me:
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#include <iostream>
#include <cmath>
using namespace std;

int main()
{
char end;
int prime, choice;
double i, sum;
double x, Y;
top:
cout << "Hello welcome to My all in one handy helper!" << "\n";
cout << "Please enter 1 for a sum function, 2 for a Quadractic eqation solver," << "\n" << "Or 3 for a Prime number checker." << "\n";
cin >> choice;
if(choice == 1) {
cout << "This is a sum function.";
cout << "Please enter a starting value" << "\n";
cin >> x;
cout << "Please enter an ending value" << "\n";
cin >> Y;
sum = 0;
for(i = x; i <= Y; i++){
sum = sum + i; //cout << i << ", " << sum << "\n"; <-- Tells the user the sum for each steps.
}
cout << "The sum from " << x << " to " << Y << " is " << sum << "\n";
sum = 1;
for(i = x; i <= Y; i++){
sum = sum*i;
}
cout << "The product from " << x << " through " << Y << " is "<< sum << "\n";
}
if(choice == 3)
{
int x, i;
cout << "Welcome to My Prime Number Calculator! \n";
cout << "Please enter an odd number and I'll tell you if it is prime! \n";
cin >> x;
prime = 1;
for(i = 3; i < x; i = i+2 ){
if(x % i == 0){
cout << i << " is a factor \n";
prime = 0;
}
}
if(prime == 0) {
cout << x << " is not a prime number";
}
else
{
cout << x << " is a prime number";
}
}
cout << "Start again? (y/n)";
cin >> end;
if(end == 'y')
{
goto top;
}
return 0;
}

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When programming, make sure to look over your code and think a little. Ask yourself, how is it going to execute itself?

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//code
if(GetAsyncKeyState(VK_NUMPAD0))
{
//stuff
}
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In this case, it does a single check to see if NUMPAD0 was pressed, how long do you have to press the button? Not long enough for sure.

Solution:
Wrap it in a loop.

Most valid requests we get here require entire revision rather than guidance on one malfunctioning aspect, so things are usually pretty dull handling tedious rudimentary beginner concepts and revising things for them.
~
Nothing wrong with that if they learn something of course, but I got tired of doing this.

Hmm, I like helping anyway.