Euler problem 40

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

analyse:

A picture tells more than a thousand words.

int b =       1          2              3                4

int c =   <-9x1=9-><--90x2=180--><--900x3=2700--><--9000x4=36000--><--enz-->

        0.12345678910......97..99100..........9991000..........999910000....

int o =   1        10      ^^    190             2890          ^^^^38890

int f = (x / b + p) = ---> 97

int e = (x % b) = -------------------------------------------> 0123

int p =   1        10            100             1000              10000

Problem40 =         210 elapsed time:    0 ms. Test Passed.