(Problem 40)Champernowne's constant

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

0.123456789101112131415161718192021...

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

If dn represents the nth digit of the fractional part, find the value of the following expression.

d1

d10

d100

d1000

d10000

d100000

d1000000

#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