b[o] = ".,-~:;=!*#$@" [N > 0 ? N : 0];

This line of code is looping through the string b[o], which consists of multiple characters. The string b[o] is being looped through from index 0 to the length of the string b[o]. If the index is greater than 0 the index that is being checked is returned, otherwise, 0 is returned.