C++ program to calculate the standard deviation of given range

#include<iostream>
#include<conio.h>
#include<math.h>

int main()
{
    system("cls");

    int i,j,a[10] = {1,2,3,4,5,6,7,8,9,10};
    float sd,sum,pr,res,sum1,count,div,res1;

    sum = 0;
    res = 0;
    count = 0;

    for(j=1;j<=9;j++)
    {
        sum = sum+a[j];
        pr = a[j]*a[j];
        count = count + pr;
        res = res + pr;
        div = count/10;
        sum1 = (sum*sum)/(10*10);
        res1 = div-sum1;
        sd = sqrt(res1);

        std::cout<<a[j]<<"t"<<pr<<"t"<<pr-a[j]<<std::endl;
    }

    std::cout<<"The standard deviation of series = "<<sd;

    getch();
    return 0;
}

2       4       2
3       9       6
4       16      12
5       25      20
6       36      30
7       49      42
8       64      56
9       81      72
10      100     90
The standard deviation of series = 3.039737