int A[100];      // A[i] = 0 means false, A[i] = 1 means true

int i = k/32;            // i = array index (use: A[i])
int pos = k%32;          // pos = bit position in A[i]

unsigned int flag = 1;   // flag = 0000.....00001
flag = flag << pos;      // flag = 0000...010...000   (shifted k positions)

A[i] = A[i] | flag;      // Set the bit at the k-th position in A[i]