(Problem 40)Champernowne's constant

An irrational decimal fraction is created by concatenating the positive integers:

0.123456789101112131415161718192021...

It can be seen that the 12^th digit of the fractional part is 1.

If d_n represents the n^th digit of the fractional part, find the value of the following expression.

d₁  d₁₀  d₁₀₀  d₁₀₀₀  d₁₀₀₀₀  d₁₀₀₀₀₀  d_1000000

#include <stdio.h>

int solve()
{
    int i, k, result, n, t, temp;
    int s[8], a[101];
    i = k = 0;
    n = result = 1;
    t = 0;
    while(1) {
        temp = n;
        i = 0;
        while(temp) {
            s[i++] = temp % 10;
            temp /= 10;
        }
        i--;
        while(i >= 0) {
            a[k] = s[i];
            t++;
            if(t == 1 || t == 10 || t == 100 || t == 1000 || t == 10000 || t == 100000 || t == 1000000) {
                result *= a[k];
                if(t == 1000000)  return result;
            }
            if(k == 100) {
                k = 1;
            } else {
                k++;
            }
            i--;
        }
        n++;
    }
}

int main(void)
{
    printf("%d\n",solve());
    return 0;
}

 

Answer:

210