If a function does not return any values, you declare its type as void:
void printResults( . . . );
If a function doesn't take any parameters as input, you declare its parameter list as void:
void ringBell(void);
If a function returns a single value, you declare its type to be the same as the type you are returning:
int getValueFromUser(. . .);
char getLetterGrade(. . .);
float calculateGPA( . . .);
If a function returns more than one value, you declare its type as void, and declare its output parameters as reference parameters of the same types you want to return:
void getSides(int &length, int &width);
void getScores(float &exam1,
float &exam2,
float &exam3,
float &exam4);