1. functions
Extra Examples

2. 6. Function type – example (1)
In the above example, the function returns the area of the circle.
Since area is defined in the function as double, then the function is of type double.
double Circle (double radius) {
double PI = 3.14;
double area;
area = * radius * radius;
return (area); }
Dr. Soha S. Zaghloul 2

3. 7. Function type – example (2)
The above function should print letter ten times on ten lines.
Since it does not return anything, then the type of the function is void.
No return statement should be associated with a function of type void.
void PrintLetter (char letter) {
int i;
for (i= 1; i<= 10; i++)
printf (“/n”, letter); }
Dr. Soha S. Zaghloul 3

4. 9. Function arguments – example (1)
In the above example, the parameter list consists of one variable radius, which is of type double.
Note that radius is not declared within the function.
double Circle (double radius) {
double PI = 3.14;
double area;
area = * radius * radius;
return (area); }
Dr. Soha S. Zaghloul 4

5. 10. Function arguments – example (2)
In the above example, the parameter list consists of two variables sum (of type double), and count (of type int)
Arguments are separated by commas.
Note that the return statement may include an arithmetic operation.
double Average (double sum, int count) {
return (sum/count); }
Dr. Soha S. Zaghloul 5

6. 11. Function arguments – example (3)
The above function contains no arguments, and is of type void.
It is called to display the shown menu.
void Menu(void) {
printf (“ +: Addition \n”);
printf (“ -: Subtraction \n”);
printf (“ *: Multiplicaiton \n”);
printf (“ /: Division \n”);
printf (“ %: Modulus \n”); }
Dr. Soha S. Zaghloul 6

7. 13. Function statements – example (1)
The above example could be written as:
The above function has only one return statement. There is no declaration, initialization, nor processing.
int Sum (int num1, int num2, int num3) {
int total;
total = num1 + num2 + num3;
return (total); }
int Sum (int num1, int num2, int num3) {
return (num1 + num2 + num3); }
Dr. Soha S. Zaghloul 7

8. Functions are defined after the end of the main function
14. Functions defintion
#include <stdio.h>
int main (void) {
------
} // end main
// start define all functions
double CircleArea (double radius)
} // end CircleArea
// end of program
Functions are defined after the end of the main function
Dr. Soha S. Zaghloul 8

9. 15. Functions prototypes
#include <stdio.h>
// Function prototype
double CircleArea(double radius);
int main (void) {
------
} // end main
// start define all functions
double CircleArea (double radius)
} // end CircleArea
// end of program
In addition, a prototype of the function should be written before the main function.
Dr. Soha S. Zaghloul 9

10. 16. Function call – EXAMPLE (1)
#include <stdio.h>
// Function prototype
double CircleArea(double radius); // FUNCTION PROTOTYPE
int main (void) {
double circle, r;
printf (“Enter circle radius> “);
scanf (“%f”, r);
circle = CircleArea( r ); // FUNCTION CALL
printf (“Area of circle = %f”, circle);
} // end main
// start define your functions
double CircleArea (double radius) // FUNCTION HEADER AND DEFINITION
double area;
area = 3.14 * radius * radius;
return (area); // RETURN VALUE
} // end CircleArea
// end of program
Dr. Soha S. Zaghloul 10

11. 19. multi-arguments Functions – EXAMPLE (1)
#include <stdio.h>
// Function prototype
int power(int num1, int num2); // FUNCTION PROTOTYPE
int main (void) {
int result;
result = power (2, 5) ; // actual parameters  num1 = 2, num2 = 5 (ie 25 = 32)
result = power (5, 2); // actual parameters  num1 = 5, num2 = 2 (ie 52 = 25)
} // end main
// start define your functions
int power( int num1, int num2) // formal parameters
int i;
int product = 1;
for (i= 1; i< num2; i++)
product *= num1;
return product;
} // end power
// end of program
Dr. Soha S. Zaghloul 11

12. 20. zer0-argument Functions – EXAMPLE (1)
#include <stdio.h>
// Function prototype
char DisplayMenu (void); // FUNCTION PROTOTYPE
int main (void) {
char option;
option = DisplayMenu() ; // FUNCTION CALL
} // end main
// start define your functions
char DisplayMenu (void) // FUNCTION HEADER
char choice;
printf (“C: Area of a Circle \n”);
printf (“T: Area of a Triangle \n”);
printf (“S: Area of a Square \n”);
printf (“ Enter your choice> “);
scanf (“%c”, choice);
return (choice); // returned value
} // end DisplayMenu
// end of program
Dr. Soha S. Zaghloul 12

13. 21. zero-argument Functions – EXAMPLE (1)
#include <stdio.h>
// Function prototype
char DisplayMenu (void); // FUNCTION PROTOTYPE
int main (void) {
char option;
option = DisplayMenu() ; // FUNCTION CALL
} // end main
// start define your functions
char DisplayMenu (void) // FUNCTION HEADER
char choice;
printf (“C: Area of a Circle \n”);
printf (“T: Area of a Triangle \n”);
printf (“S: Area of a Square \n”);
printf (“ Enter your choice> “);
scanf (“%c”, choice);
return (choice); // returned value
} // end DisplayMenu
// end of program
Dr. Soha S. Zaghloul 13

14. 22. self-check exercise
Write a complete modular program that displays a menu to perform the four mathematical operations (+, -, *, /). Each operation should be then computed in a separate function.
Dr. Soha S. Zaghloul 14