http://projecteuler.net/problem=40 [Answer:210]

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#include <iostream>using namespace std;int NthDigit( int n ){    int nNumberLength = 1;    int nNumberCount = 9;    int nNumberBegin = 1;    while ( n > nNumberLength * nNumberCount )    {        n -= nNumberLength * nNumberCount;        nNumberLength += 1;        nNumberCount *= 10;        nNumberBegin *= 10;    }    int nIndex = (n - 1) / nNumberLength;    int nNumber = nNumberBegin + nIndex;    int times = (nNumberLength - 1) - ((n - 1) - nIndex * nNumberLength);    while ( times > 0 )    {        --times;        nNumber /= 10;    }    return nNumber % 10;} int main(){    int result = 1;    result *= NthDigit( 1 );    result *= NthDigit( 10 );    result *= NthDigit( 100 );    result *= NthDigit( 1000 );    result *= NthDigit( 10000 );    result *= NthDigit( 100000 );    result *= NthDigit( 1000000 );    cout << result << endl;    return 0;}