// addCommaToNumberString: // The In-/Output Buffer char* numberString has to be large enough to contain additional commas // int length is the length of the input string (or amount of digits) void addCommaToNumberString( char* numberString, int &length ) { int readPos = length - 1; // pos is the index of the last digit in the remaining string to work on length += readPos / 3; // !Integer Division! ~ Add the amount of commas that will be added to the length int writePos= length - 1; while( readPos > 2 ) // For each tripple of digits: { numberString[ writePos - 0 ] = numberString[ readPos - 0 ]; numberString[ writePos - 1 ] = numberString[ readPos - 1 ]; numberString[ writePos - 2 ] = numberString[ readPos - 2 ]; numberString[ writePos - 3 ] = ','; readPos -= 3; writePos -= 4; } }