1. Lecture3

2. Lecture Outline Program Layout Executable Statements
Input/Output Statements
Input/Output Operation
scanf function
printf function
Assignment Statements
Arithmetic Operations
The Return Statement
Comments in Programs
A Complete C Program
Mixed Data Types in Assignment Statements
Expressions with multiple operators
Rules for Expression Evaluation
Writing mathematical Formulas in C
Types of Errors

3. Program Layout provides an instruction to the preprocessor.
Preprocessor Directive
int main(void) {
Declaration
Executable Statements }
A C program line beginning with # that
provides an instruction to the preprocessor.
Examples: #include, #define.
Function main indicates the start of the
program.
The part of a program that tells the
compiler the names of memory cells and
their data types.
Program commands that are converted to
machine code by the compiler.

4. Executable Statements
Getting information in and out of a program.
Input/Output Statements (functions)
Doing calculations.
Assignment Statements

5. Input/Output Operations
Input Operation
An instruction that copies data from an input device into memory.
Output Operation
An instruction that displays information stored in memory.

6. Input/Output Functions
Input Functions
Perform input operations.
Example: scanf.
Output Functions
Perform output operations.
Example: printf.

7. scanf
The scanf function gets data entered by the user and copies it into
memory.
Syntax
scanf(format string, input list);
Example
scanf("%c%i", &firstinitial, &age);
H32
placeholder

8. Placeholder
A placeholder is a symbol beginning with % in a format string that
indicates where to display the output value.
Placeholder Variable Type Function Use
%c char printf/scanf
%i or %d int printf/scanf
%f float printf/scanf

9. Examples scanf("%i",&workhours); scanf("%c",&letter);
scanf("%i",&student_ID);
scanf("%f",&tot_score);
scanf("%f",&temperature);
scanf("%f",&working_hours);
scanf("%i%c",&population,&firstinitial);

10. printf The printf function displays information on the screen. Syntax
printf(format string);
printf(format string, print list);
Note: a format string is always enclosed in " "
placeholder
newline
escape sequence
Example
printf("That equals %fKilometers.\n",kms);
function
name
format
string
print
list

11. New Line Escape Sequence "\n"
Is the newline escape sequence symbol which is placed in a printf
to skip to a new line.

12. Examples printf("Please enter the student's grades:");
printf("The class average is %f ",average);
The class average is 95.5.
printf("The total area is %f and the total cost is %i S.R.",tarea,tcost);
The total area is 60.2 and the total cost is 4530 S.R.
printf("The student received an %c grade in the course.",grade);
The student received an A grade in the course.

13. Examples (Continue) printf("The grade is %c%c", grade, gradesymb);
The grade is A+
printf("I am the first line\n");
printf("\n I am the second line\n");
I am the first line
I am the second line

14. Formatting Numbers in Program Output
Value Format Displayed Output
%4i
%5i
%1i
%4i
%5i
%2i

15. Formatting Numbers in Program Output
Value Format Displayed Output
%6.2f
%6.2f
%6.2f
%6.2f
%6.2f
%6.2f

16. Formatting Numbers in Program Output
Value Format Displayed Output
%5.2f
%3.2f
%4.2f
%.3f
%4.2f
%.4f

17. Assignment Statements
It stores a value or a computational result in a variable.
It is used to perform most arithmetic operations in a program.
Variable=expression;
Syntax
Examples
Total_Grades = Grade1 + Grade2 + Grade3;
No_Students = 3;
Average = Total_Grades / No_Students;

18. Arithmetic Expressions
Arithmetic Meaning
Operator
addition
subtraction
* multiplication
/ division
% remainder

19. The % Operation (Remainder)
Examples
3 % 5 = 3
4 % 5 = 4
5 % 5 = 0
6 % 5 = 1
7 % 5 = 2
8 % 5 =3
5 % 3 = 2
5 % 4 = 1
15 % 5 = 0
15 % 6 = 3

20. C Language Elements #include <stdio.h>
#define KMS_PER_MILE 1.609
int main(void) {
float miles, kms;
printf("Enter the distance in miles: ");
scanf("%f", &miles);
kms = KMS_PER_MILE * miles;
printf("That equals %.2f kilometers.\n", kms);
return(0); }

21. The Return statement
The return statement transfers control from a function back to the
activator of the function.
For function main, control is transferred back to the operating
system
The value of expression is returned as the result of the function
execution.
Syntax
return expression;
Example
return(0);

22. Comments in programs Syntax /* comment text*/ Examples
/* This is a one line comment */ /*
* This is a multiple line comment in which the stars not immediately
* proceeded or followed by slashes have no special syntactic
* significance */

23. A Complete C Program /* converts distances from miles to kilometers */
#include <stdio.h> /* printf, scanf definitions */
#define KMS_PER_MILE /* conversion constant */
int main(void) {
float miles, /* distance in miles */
kms; /* equivalent distance in kilometers */
/* get the distance in miles */
printf("Enter the distance in miles: ");
scanf("%f", &miles);
/* convert the distance to kilometers */
kms = KMS_PER_MILE * miles;
/* display the distance in kilometers */
printf("That equals %.2f kilometers.\n", kms);
return(0); }

24. Mixed Data Types in an Assignment Statement
The variable to the left of the equals sign determines the data types
of an expression.
Example: if x is int and y is float then
x = 7 * 0.5; 3
y = 7 * 0.5;
3.50
x = 100/5; 20
y = 100/5;
20.00

25. Expressions with multiple operators
Operators with multiple operators are common in C.
Example: x = b * b - 4 * a * c
These expressions can include:
Unary operators:
Take only one operand.
Example: x = -y;
p = +x * y
Binary operators:
Requires two operands.
Example: x = y + 2;

26. Rules for Expression Evaluation
Rule # 1: Parentheses rule
All expressions in parentheses must be evaluated separately.
Nested parenthesized expressions must be evaluated from the inside
out.
Example:
( ( a + b ) / ( c + d ) ) * 2

27. Rules for Expression Evaluation
Rule # 2: Operator precedence rule
Operators in the same expression are evaluated in the following
order:
unary + , - first
* , / , % next
binary + , - last
Example:
a + b * c

28. Rules for Expression Evaluation
Rule # 3: Associativity rule
Right associativity: unary operator in the same sub-expression and
at the same level (such as + and -) are evaluated right to left.
Example:
a + b - c
Left associativity: Binary operator in the same sub-expression and
at the same level (such as + and -) are evaluated left to right.

29. Rules for Expression Evaluation (Examples)
z - ( a + b / 2 ) + w * - y
( b * b ) - ( 4 * 4 ) * ( a * c )
A * - ( b + c )

30. Writing Mathematical Formulas in C
Always specify multiplication explicitly by using the operator *
where needed.
Example: b² - 4 a c = b * b - 4 * a * c
Use parentheses when required to control the order of operator
evaluation.
Example: a + b = ( a + b ) / ( c + d )
c + d
Two arithmetic operators can be written in succession if the second
is a unary operator
Example: a x - ( b + c ) = a * - ( b + c )

31. Writing Mathematical Formulas in C (Examples)
a + b - c
= a + b - c 1
1 + a²
= 1 / ( 1 + a * a)
a x (5b + c)
= a * ( 5 * b + c )

32. Types of Errors
Syntax error: a violation of the C grammar rules. Detected during
compilation.
Logic error: an error caused by following an incorrect algorithm.
Run-time Error: an attempt to perform an invalid operation,
detected during program execution.
Example: dividing a number by zero.