求a + aa + aaa + aaaa + aaaaa ...的值，例如：1 + 11 + 111，2 + 22 + 222 + 2222 + 22222

#include <stdio.h>

unsigned superposition(unsigned m, unsigned n);

int main()

{

    printf("1 + 11 + 111 + 1111 + 11111 = %u
", superposition(1, 5));

    printf("2 + 22 + 222 + 2222 + 22222 + 222222 = %u
", superposition(2, 6));

    printf("3 + 33 + 333 + 3333 + 33333 + 333333 + 3333333 = %u
", superposition(3, 7));

    return 0;

}

unsigned superposition(unsigned m, unsigned n)

{

    unsigned u = 0, sum = 0;

    for (unsigned i = 0; i < n; ++i)

    {

        u = u * 10 + m;

        sum += u;

    }

    return sum;

}