C and C++ program to find the sum of a GP (Geometric progression)

#include "iostream.h"
#include "conio.h"
// Function to calculate the exponential values
int expo(int power, int base)
{
 int prod = 1, i = 1;
 while (i<=power)
 {
  prod = prod * base;
  i++;
 }
 return(prod);
}
void s3()
{
 int n, a, r, i = 1, exp;
 float term, sum = 0;
 cout << "\n\tEnter the value of n in the series ";
 cout << "\n\t a + ar + ar^2 +...+ ar^(n-1) ";
 cin >> n;
 cout << "\n\tEnter the value of a in the series ";
 cout << "\n\t a + ar + ar^2 +...+ ar^(n-1) ";
 cin >> a;
 cout << "\n\tEnter the value of r in the series ";
 cout << "\n\t a + ar + ar^2 +...+ ar^(n-1) ";
 cin >> r;
 while(i<=n)
 {
  exp = expo((i - 1), r);
  term = float(a * exp);
  sum = sum + term;
  i++;
 }
 cout << "\n\n\tThe sum is " << sum;
}
void main()
{
 clrscr();
 s3();
}
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