1. Lecture4

2. Lecture Outline Functions Logical Operators If statement
Compound if Statement
Exercise
Debugging

3. Functions A function is a subprogram that performs a specific task.
Functions you know:
printf("Hi");
scanf("%i",&number);

4. Pre-defined and User-defined Functions
Pre-defined Function
Is a function that is already defined in one of the many C libraries.
It is included in the program through the preprocessor directive
statement #include< > and used in the program to perform a
specific task.
Ex: #include<stdio.h>
Defines printf & scanf functions
User-defined Function
Is a function that is created by the user.
It is defined before the main program through a function prototype
and called upon in the main program to perform a specific task.

5. Pre-defined Functions
Arithmetic Functions
Are functions that perform arithmetic operations.
They are usually located in the math.h or stdlib.h libraries.
Examples
abs(x) is a function that returns the absolute value of its integer
argument.
sqrt(x) is a function that returns the square root of x.

6. Pre-defined Functions
Function call in an Assignment Statement
Syntax
Y = function name(argument);
Example
Y = sqrt(x);
function call x y
square root
computation
function sqrt

7. Pre-defined Functions
Examples
x = -5
y = abs(x)
y = 5
x = 90
y = abs(x) + 2
y = 92
x = 10
y = sqrt(x + 6)
y = 4
x = 2.25
y = sqrt(x)
y = 1.25

8. Square Root Program /* Performs a square root computation */
#include <stdio.h> /* definitions of printf, scanf */
#include <math.h> /* definition of sqrt */
int main(void) {
float number; /* input/output variable */
/* Get a number and display its root. */
printf("Enter a number: ");
scanf("%f", &number);
number = sqrt(number);
printf("The square root of this number is %.2f\n", number);
return(0); }

9. Relational and Equality Operators
== equal to
!= not equal to
Relational
< less than
> greater than
<= less than or equal to
>= grater than or equal to

10. Logical Operators The && Operator (and)
Operand1 Operand2 Operand1 && Operand 2
nonzero(true) nonzero(true) 1(true)
nonzero(true) 0(false) (false)
0(false) nonzero(true) 0(false)
0(false) 0(false) (false)

11. Logical Operators The || Operator (or)
Operand1 Operand2 Operand1 && Operand 2
nonzero(true) nonzero(true) 1(true)
nonzero(true) 0(false) (true)
0(false) nonzero(true) 1(true)
0(false) 0(false) 0(false)

12. Logical Operators The ! Operator (not) Operand1 Operand2
nonzero(true) 0(false)
0(false) 1(true)

13. Operator Precedence Operator Precedence function calls highest
! + - & (unary operators)
* / %
+ -
< <= >= >
== !=
&& ||
= lowest

14. Examples on Relational, Equality, and Logical Operators
x = y= z=2
Expressions Evaluation Value
x==1 || x== || (True)
(x==1) || (x==3) || 1 1 (True)
!(z>=2) !(1) (False)
!!(y==4) !!(1) !(0) (True)
(z>=2) && (x<10) && 1 1 (True)
(y!=4) (False)

15. Examples English language: x less than or equal to 0
C language: x<=0
English language: grade not equal to 'A'
C language: grade != 'A'
English language: an exam score of 90 and above or quiz
score of 95 and above
C language: exam>=90 || quiz>=95
English language: a single man whose 55 years old or older
C language: status=='s'&&gender=='m' &&age>=55

16. if Statement Syntax if (condition) statement;
if (condition) statement; else statement;
Examples
if (num_stud==25)
printf("The class is full");
else
printf("The class is not full");
if (score>=90) grade='A';

17. More Examples if (choice==1) printf("Your choice is 1");
if (score>=90 && attendance==95) grade='A';
if (day==29 || day==30) printf ("Happy Eid");
if (mood=='g')
printf("Have a good day!");
else
printf("Have a bad day!");

18. Exercise 1
Write a program that accepts a type of fruit from the user and displays the market the user should go to based on the following:
apples  Azizia
all other fruits  Fruit Market

19. Exercise 1 #include<stdio.h> int main(void) {char fruit;
printf("Enter a fruit: ");
scanf("%c", &fruit);
if (fruit=='a')
printf("Go to Azizia!\n");
else
printf ("Go to the fruit market!\n");}

20. Compound if Statement Syntax if (condition) {statements}
if (condition) {statements} else {statements}

21. Comparing if Statement Syntax
Simple if statement
if (condition) statement;
if (condition) statement; else statement;
Compound if statement
if (condition) {statements}
if (condition) {statements} else statements}

22. Exercise 1
Write a program that calculates the discount, if any, on a sale. Sales of $100 and over are eligible for a 10% discount. The program should ask the user what the amount of their purchase is and calculates and displays the discount, if there is any, or else it will display a message stating that there is no discount.

23. Exercise 1 #include<stdio.h> int main(void) {float price;
printf("Enter the price: ");
scanf("%f", &price);
if (price>=100) {
price=price*0.9;
printf("The price after the discount is: %.2f\n", price); }
else
printf("There is no discount\n");
return(0);}

24. Debugging Debugging is the process of finding errors in a program.
Diagnostic printfs are statements placed in areas of the program
where a programmer ‘thinks’ she made a mistake. It can be used
to view the variable contents at any time.