Encryption arrays in C -

i having trouble encryption function in c. char data[] holds 4 characters (i.e. byte) trying encrypt using ciphermap[] found using random number generator. basically, nonsense[] encrypted array , it's index equal ciphermap's value...given this, not sure how set encrypted value byte of particular spot original char data[].

i know question may confusing or vague that's because confused...and new @ such low-level programming. here code:

int encrypt (char data[]) // plain text in char {   int nonsense[28]; // cipher text   int i;   (i = 0; < 28; i++)   {     nonsense[ciphermap[i]] = data[i / 7] & (1 << (i % 7));     printf("%d", nonsense[ciphermap[i]]);   }   return 1; } 

the problem expression data[i / 7] & (1 << (i % 7)) yields single bit, leaves bit @ it's original location. result of expression power of 2 (1, 2, 4, etc). here's different way extract bits.

void encrypt (char data[]) // plain text in char {     int nonsense[28]; // cipher text     int i, mask, index;      index = 0;     ( = 0; < 4; i++ )     {         ( mask = 1; mask < 128; mask <<= 1 )         {             if ( data[i] & mask )                 nonsense[ciphermap[index]] = 1;             else                 nonsense[ciphermap[index]] = 0;             index++;         }     } } 

in code above, i array index plain text, , mask one-bit value that's used check bits in data. mask starts value of 1 (lsb first) , shifted left 1 bit each time through loop. when mask reaches msb, have value of 128, terminates inner loop , allows outer loop move on next input byte. 7 least significant bits of each byte encoded.