recording the value of a variable - c++

Question

I was wondering how would one record the previous value of a variable that changes. An example of this problem is this code down below:
int distanceFormula(int x1, int x2, int y1, int y2){
int distance;
distance = sqrt(pow((x1-x2), 2) + pow((y1-y2), 2));
return distance;
}
int main(){
for(int i = 0; i < 2; i++){
int x = rand() % 180;
int y = rand() % 180;
int x2 = rand() % 180;
int y2 = rand() % 180;
int distance = distanceFormula(x, x2, y, y2);
int priordistance = distanceFormula(x, x2, y, y2);
if(priordistance != distance){
cout<<"Yes! It worked!"<<endl;
}
}
return 0;
}
The code itself won't return "Yes! It worked!" How would one record the previous value of distance and then compare that previous value to the current value?
Edit:
Thanks for the fast comments! Really appreciate it.
To clarify the actual question, the code above is just a quick template/example. Since the value of distance will change upon the second loop around, how would one RECORD the first value of distance and set that value to priordistance and then compare the current value of distance to priordistance (whose value is really just the previous value of distance).

Answer 1

Simply redord the previous value in a variable.
#include <cmath>
#include <cstdlib>
#include <iostream>
using std::cout;
using std::endl;
int distanceFormula(int x1, int x2, int y1, int y2){
int distance;
distance = sqrt(pow((x1-x2), 2) + pow((y1-y2), 2));
return distance;
}
int main(){
int priordistance = 0; // a variable used to record the value
for(int i = 0; i < 2; i++){
int x = rand() % 180;
int y = rand() % 180;
int x2 = rand() % 180;
int y2 = rand() % 180;
int distance = distanceFormula(x, x2, y, y2);
if(i > 0 && priordistance != distance){ // use i > 0 to avoid compareing with meaningless value
cout<<"Yes! It worked!"<<endl;
}
priordistance = distance; // record the value
}
return 0;
}

Answer 2

There is a few ways you could do this... you could define priordistance outside of your for loop, and be sure to only redefine it 1 time (since you are looping twice).
However this is not what I would do, I would simply create an array of integers that hold n number of 'distances' for your reference by index i
int[] or int *

Answer 3

You can do various things. You need the value to persist throughout your for loop. Note that there is no point in comparing until you have already got one prior value.
int main(){
int priordistance = 0; //lifetime outside for loop
for(int i = 0; i < 2; i++){
int x = rand() % 180;
int y = rand() % 180;
int x2 = rand() % 180;
int y2 = rand() % 180;
int distance = distanceFormula(x, x2, y, y2);
if(i && priordistance != distance){
//^---- have we got a prior value yet?
cout<<"Yes! It worked!"<<endl;
}
priordistance = distance;//remember for next time
}
return 0;
}

Answer 4

Do you mean something like the following?
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <cmath>
int distanceFormula( int x1, int x2, int y1, int y2 )
{
int distance;
distance = std::sqrt( std::pow( x1 - x2, 2 ) + std::pow( y1 - y2, 2 ) );
return distance;
}
int main()
{
const size_t N = 2;
int distance[N];
std::srand( ( unsigned int )std::time( nullptr ) );
for ( size_t i = 0; i < N; i++ )
{
int x = rand() % 180;
int y = rand() % 180;
int x2 = rand() % 180;
int y2 = rand() % 180;
distance[i] = distanceFormula( x, x2, y, y2 );
}
if ( distance[0] != distance[1] ) std::cout << "Yes! It worked!" << std::endl;
return 0;
}
The program output is
Yes! It worked!