Chap 2 Introduction to C ProgrammingFile.pdf

 2007 Pearson Education, Inc. All rights reserved.
1
2
2
Introduction
to C Programming

2
What's in a name? That which we call a rose
By any other name would smell as sweet.
—William Shakespeare
Romeo and Juliet
When faced with a decision, I always ask,
“What would be the most fun?”
—Peggy Walker

3
“Take some more tea,” the March Hare said to
Alice, very earnestly. “I’ve had nothing yet,”
Alice replied in an offended tone: “so I can’t take
more.” “You mean you can’t take less,” said the
Hatter: “it’s very easy to take more than nothing.”
—Lewis Carroll
High thoughts must have high language.
—Aristophanes

4
OBJECTIVES
In this chapter you will learn:
 To write simple computer programs in C.
 To use simple input and output statements.
 The fundamental data types.
 Computer memory concepts.
 To use arithmetic operators.
 The precedence of arithmetic operators.
 To write simple decision-making statements.

5
2.1 Introduction
2.2 A Simple C Program: Printing a Line of Text
2.3 Another Simple C Program: Adding Two Integers
2.4 Memory Concepts
2.5 Arithmetic in C
2.6 Decision Making: Equality and Relational Operators

6
2.1 Introduction
 C programming language
– Structured and disciplined approach to program design
 Structured programming
– Introduced in chapters 3 and 4
– Used throughout the remainder of the book

 2007 Pearson Education,
Inc. All rights reserved.
7
1 /* Fig. 2.1: fig02_01.c
2 A first program in C */
3 #include <stdio.h>
4
5 /* function main begins program execution */
6 int main( void )
7 {
8 printf( "Welcome to C!n" );
9
10 return 0; /* indicate that program ended successfully */
11
12 } /* end function main */
Welcome to C!
Outline
fig02_01.c
/* and */ indicate comments – ignored by compiler
#include directive tells C to load a particular file
Left brace declares beginning of main function
Statement tells C to perform an action
return statement ends the function
Right brace declares end of main function

8
2.2 A Simple C Program:
Printing a Line of Text
Comments
– Text surrounded by /* and */ is ignored by computer
– Used to describe program
 #include <stdio.h>
– Preprocessor directive
- Tells computer to load contents of a certain file
– <stdio.h> allows standard input/output operations

 // stdafx.cpp : source file that includes just the
standard includes
 // ct71.pch will be the pre-compiled header
 // stdafx.obj will contain the pre-compiled type
information
9

10
Common Programming Error 2.1
Forgetting to terminate a comment with */.

11
Starting a comment with the characters */
or ending a comment with the characters /*.

12
 int main()
– C++ programs contain one or more functions, exactly one
of which must be main
– Parenthesis used to indicate a function
– int means that main "returns" an integer value
– Braces ({ and }) indicate a block
- The bodies of all functions must be contained in braces

13
Good Programming Practice 2.1
Every function should be preceded by a
comment describing the purpose of the
function.

14
 printf( "Welcome to C!n" );
– Instructs computer to perform an action
- Specifically, prints the string of characters within quotes ("
")
– Entire line called a statement
- All statements must end with a semicolon (;)
– Escape character ()
- Indicates that printf should do something out of the ordinary
- n is the newline character

15
Escape sequence Description
n Newline. Position the cursor at the beginning of the next line.
t Horizontal tab. Move the cursor to the next tab stop.
a Alert. Sound the system bell.
Backslash. Insert a backslash character in a string.
" Double quote. Insert a double-quote character in a string.
Fig. 2.2 | Some common escape sequences.

16
Typing the name of the output function
printf as print in a program.

17
 return 0;
– A way to exit a function
– return 0, in this case, means that the program terminated
normally
 Right brace }
– Indicates end of main has been reached
 Linker
– When a function is called, linker locates it in the library
– Inserts it into object program
– If function name is misspelled, the linker will produce an error
because it will not be able to find function in the library

18
Add a comment to the line containing the
right brace, }, that closes every function,
including main.

19
The last character printed by a function that
displays output should be a newline (n).
This ensures that the function will leave the
screen cursor positioned at the beginning of a
new line. Conventions of this nature
encourage software reusability—a key goal in
software development environments.

20
Indent the entire body of each function one
level of indentation (we recommend three
spaces) within the braces that define the
body of the function. This indentation
emphasizes the functional structure of
programs and helps make programs easier
to read.

21
Set a convention for the size of indent you
prefer and then uniformly apply that
convention. The tab key may be used to create
indents, but tab stops may vary. We
recommend using three spaces per level of
indent.

22
1 /* Fig. 2.3: fig02_03.c
2 Printing on one line with two printf statements */
4
6 int main( void )
7 {
8 printf( "Welcome " );
9 printf( "to C!n" );
10
12
Welcome to C!
Outline
fig02_03.c
printf statement starts printing from where
the last statement ended, so the text is
printed on one line.

23
1 /* Fig. 2.4: fig02_04.c
2 Printing multiple lines with a single printf */
4
6 int main( void )
7 {
8 printf( "WelcomentonC!n" );
9
11
Welcome
to
C!
Outline
fig02_04.c
Newline characters move the cursor to the next line

24
1 /* Fig. 2.5: fig02_05.c
2 Addition program */
4
6 int main( void )
7 {
8 int integer1; /* first number to be input by user */
9 int integer2; /* second number to be input by user */
10 int sum; /* variable in which sum will be stored */
11
12 printf( "Enter first integern" ); /* prompt */
13 scanf( "%d", &integer1 ); /* read an integer */
14
15 printf( "Enter second integern" ); /* prompt */
16 scanf( "%d", &integer2 ); /* read an integer */
17
18 sum = integer1 + integer2; /* assign total to sum */
19
20 printf( "Sum is %dn", sum ); /* print sum */
21
23
Enter first integer
45
Enter second integer
72
Sum is 117
Outline
fig02_05.c
Definitions of variables
scanf obtains a value from the
user and assigns it to integer1
scanf obtains a value from the
user and assigns it to integer2
Assigns a value to sum

25
2.3 Another Simple C Program:
Adding Two Integers
 As before
– Comments, #include <stdio.h> and main
 int integer1, integer2, sum;
– Definition of variables
- Variables: locations in memory where a value can be stored
– int means the variables can hold integers (-1, 3, 0, 47)
– Variable names (identifiers)
- integer1, integer2, sum
- Identifiers: consist of letters, digits (cannot begin with a digit) and
underscores( _ )
Case sensitive
– Definitions appear before executable statements
- If an executable statement references and undeclared variable it will
produce a syntax (compiler) error

26
Using a capital letter where a lowercase letter
should be used (for example, typing Main
instead of main).

27
Portability Tip 2.1
Use identifiers of 31 or fewer characters.
This helps ensure portability and can avoid
some subtle programming errors.

28
Choosing meaningful variable names
helps make a program self-documenting,
i.e., fewer comments are needed.

29
The first letter of an identifier used as a
simple variable name should be a lowercase
letter. Later in the text we will assign special
significance to identifiers that begin with a
capital letter and to identifiers that use all
capital letters.

30
Multiple-word variable names can help make a
program more readable. Avoid running the separate
words together as in totalcommissions. Rather,
separate the words with underscores as in
total_commissions, or, if you do wish to run the
words together, begin each word after the first with a
capital letter as in totalCommissions. The latter
style is preferred.

31
Placing variable definitions among
executable statements causes syntax errors.

32
Separate the definitions and executable
statements in a function with one blank line
to emphasize where the definitions end and
the executable statements begin.

33
Adding Two Integers
 scanf( "%d", &integer1 );
– Obtains a value from the user
- scanf uses standard input (usually keyboard)
– This scanf statement has two arguments
- %d - indicates data should be a decimal integer
- &integer1 - location in memory to store variable
- & is confusing in beginning – for now, just remember to
include it with the variable name in scanf statements
– When executing the program the user responds to the
scanf statement by typing in a number, then pressing the
enter (return) key

34
Place a space after each comma (,) to
make programs more readable.

35
Adding Two Integers
 = (assignment operator)
– Assigns a value to a variable
– Is a binary operator (has two operands)
sum = variable1 + variable2;
sum gets variable1 + variable2;
– Variable receiving value on left
 printf( "Sum is %dn", sum );
– Similar to scanf
- %d means decimal integer will be printed
- sum specifies what integer will be printed
– Calculations can be performed inside printf statements
printf( "Sum is %dn", integer1 + integer2 );

36
Place spaces on either side of a binary
operator. This makes the operator stand
out and makes the program more readable.

37
A calculation in an assignment statement
must be on the right side of the = operator.
It is a syntax error to place a calculation on
the left side of an assignment operator.

38
Forgetting one or both of the double quotes
surrounding the format control string in a
printf or scanf.

39
Forgetting the % in a conversion specification in
the format control string of a printf or scanf.

40
Placing an escape sequence such as n outside
the format control string of a printf or
scanf.

41
Forgetting to include the expressions
whose values are to be printed in a
printf containing conversion specifiers.

42
Not providing a conversion specifier when
one is needed in a printf format control
string to print the value of an expression.

43
Placing inside the format control string the
comma that is supposed to separate the
format control string from the expressions
to be printed.

44
Forgetting to precede a variable in a scanf
statement with an ampersand when that
variable should, in fact, be preceded by an
ampersand.

45
Preceding a variable included in a printf
statement with an ampersand when, in fact,
that variable should not be preceded by an
ampersand.

46
2.4 Memory Concepts
 Variables
– Variable names correspond to locations in the computer's
memory
– Every variable has a name, a type, a size and a value
– Whenever a new value is placed into a variable (through
scanf, for example), it replaces (and destroys) the previous
value
– Reading variables from memory does not change them

47
Fig. 2.6 | Memory location showing the name and value of a variable.

48
Fig. 2.7 | Memory locations after both variables are input.

49
Fig. 2.8 | Memory locations after a calculation.

50
2.5 Arithmetic
 Arithmetic calculations
– Use * for multiplication and / for division
– Integer division truncates remainder
- 7 / 5 evaluates to 1
– Modulus operator(%) returns the remainder
- 7 % 5 evaluates to 2
 Operator precedence
– Some arithmetic operators act before others (i.e., multiplication
before addition)
- Use parenthesis when needed
– Example: Find the average of three variables a, b and c
- Do not use: a + b + c / 3
- Use: (a + b + c ) / 3

51
C opetration
Arithmetic
operator
Algebraic
expression
C expression
Addition + f + 7 f + 7
Subtraction – p – c p - c
Multiplication * bm b * m
Division /
or or
x
x y x÷ y
y x / y
Remainder % r mod s r % s
Fig. 2.9 | Arithmetic operators.

52
An attempt to divide by zero is normally
undefined on computer systems and generally
results in a fatal error, i.e., an error that
causes the program to terminate immediately
without having successfully performed its job.
Nonfatal errors allow programs to run to
completion, often producing incorrect results.

53
Fig. 2.10 | Precedence of arithmetic operators.
Operator(s) Operation(s) Order of evaluation (precedence)
( ) Parentheses Evaluated first. If the parentheses are
nested, the expression in the innermost pair is
evaluated first. If there are several pairs of
parentheses “on the same level” (i.e., not nested),
they are evaluated left to right.
*
/
%
Multiplication
Division
Remainder
Evaluated second. If there are several, they are
evaluated left to right.
+
-
Addition
Subtraction
Evaluated last. If there are several, they are
evaluated left to right.

54
Fig. 2.11 | Order in which a second-degree polynomial is evaluated.

55
Using redundant parentheses in complex
arithmetic expressions can make the
expressions clearer.

56
2.6 Decision Making: Equality and
Relational Operators
 Executable statements
– Perform actions (calculations, input/output of data)
– Perform decisions
- May want to print "pass" or "fail" given the value of a test grade
 if control statement
– Simple version in this section, more detail later
– If a condition is true, then the body of the if statement executed
- 0 is false, non-zero is true
– Control always resumes after the if structure
 Keywords
– Special words reserved for C
– Cannot be used as identifiers or variable names

57
Standard algebraic
equality operator or
relational operator
C equality or
relational
operator
Example of
C condition
Meaning of C condition
Equality operators
= == x == y x is equal to y
≠ != x != y x is not equal to y
Relational operators
> > x > y x is greater than y
< < x < y x is less than y
≥ >= x >= y x is greater than or equal to y
≤ <= x <= y x is less than or equal to y
Fig. 2.12 | Equality and relational operators.

58
A syntax error will occur if the two symbols
in any of the operators ==, !=, >= and <=
are separated by spaces.

59
A syntax error will occur if the two symbols
in any of the operators !=, >= and <= are
reversed as in =!, => and =<, respectively.

60
Confusing the equality operator == with
the assignment operator =.

61
Placing a semicolon immediately to the right
of the right parenthesis after the condition in
an if statement.

62
Indent the statement(s) in the body of an
if statement.

63
Place a blank line before and after every
if statement in a program for readability.

64
Although it is allowed, there should be no
more than one statement per line in a program.

65
Placing commas (when none are needed)
between conversion specifiers in the format
control string of a scanf statement.

66
1 /* Fig. 2.13: fig02_13.c
2 Using if statements, relational
3 operators, and equality operators */
5
7 int main( void )
8 {
9 int num1; /* first number to be read from user */
10 int num2; /* second number to be read from user */
11
12 printf( "Enter two integers, and I will tell youn" );
13 printf( "the relationships they satisfy: " );
14
15 scanf( "%d%d", &num1, &num2 ); /* read two integers */
16
17 if ( num1 == num2 ) {
18 printf( "%d is equal to %dn", num1, num2 );
19 } /* end if */
20
21 if ( num1 != num2 ) {
22 printf( "%d is not equal to %dn", num1, num2 );
23 } /* end if */
24
25 if ( num1 < num2 ) {
26 printf( "%d is less than %dn", num1, num2 );
27 } /* end if */
28
Outline
fig02_13.c
(1 of 3 )
Checks if num1 is equal to num2
Checks if num1 is not equal to num2
Checks if num1 is less than num2

67
29 if ( num1 > num2 ) {
30 printf( "%d is greater than %dn", num1, num2 );
31 } /* end if */
32
33 if ( num1 <= num2 ) {
34 printf( "%d is less than or equal to %dn", num1, num2 );
35 } /* end if */
36
37 if ( num1 >= num2 ) {
38 printf( "%d is greater than or equal to %dn", num1, num2 );
39 } /* end if */
40
42
Enter two integers, and I will tell you
the relationships they satisfy: 3 7
3 is not equal to 7
3 is less than 7
3 is less than or equal to 7
(continued on next slide… )
Outline
fig02_13.c
(2 of 3 )
Checks if num1 is greater than num2
Checks if num1 is less than or equal to num2
Checks if num1 is greater than equal to num2

68
(continued from previous slide…)
the relationships they satisfy:
22 is not equal to 12
22 is greater than 12
22 is greater than or equal to 12
the relationships they satisfy:
7 is equal to 7
7 is less than or equal to 7
7 is greater than or equal to 7
Outline
fig02_13.c
(3 of 3 )

69
A lengthy statement may be spread over
several lines. If a statement must be split across
lines, choose breaking points that make sense
(such as after a comma in a comma-separated
list). If a statement is split across two or more
lines, indent all subsequent lines.

70
Refer to the operator precedence chart when writing
expressions containing many operators. Confirm that
the operators in the expression are applied in the
proper order. If you are uncertain about the order of
evaluation in a complex expression, use parentheses to
group expressions or break the statement into several
simpler statements. Be sure to observe that some of C’s
operators such as the assignment operator (=) associate
from right to left rather than from left to right.

71
Operators Associativity
( ) left to right
* / % left to right
+ - left to right
< <= > >= left to right
== != left to right
= right to left
Fig. 2.14 | Precedence and associativity of the operators discussed so far.

72
Keywords
auto double int struct
break else long switch
case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while
Fig. 2.15 | C’s keywords.

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