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Chapter 2 - Introduction to C Programming

Nov 02, 2012

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Chapter 2 - Introduction to C Programming. Outline 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. 2.1 Introduction.

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Chapter 2 - Introduction to C Programming Outline 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

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

1 /* Fig. 2.1: fig02_01.c 2 A first program in C */ 3 #include <stdio.h> 4 5 int main() 6 { 7 printf( "Welcome to C!\n" ); 8 9 return 0; 10 } 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 Welcome to C!

2.2 A Simple C Program:Printing a Line of Text • 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

2.2 A Simple C Program:Printing a Line of Text • 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

2.2 A Simple C Program:Printing a Line of Text • return0; • A way to exit a function • return0, 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

1 /* Fig. 2.5: fig02_05.c 2 Addition program */ 3 #include <stdio.h> 4 5 int main() 6 { 7 int integer1, integer2, sum; /* declaration */ 8 9 printf( "Enter first integer\n" ); /* prompt */ 10 scanf( "%d", &integer1 ); /* read an integer */ 11 printf( "Enter second integer\n" ); /* prompt */ 12 scanf( "%d", &integer2 ); /* read an integer */ 13 sum = integer1 + integer2; /* assignment of sum */ 14 printf( "Sum is %d\n", sum ); /* print sum */ 15 16 return 0; /* indicate that program ended successfully */ 17 } 1. Initialize variables 2. Input 2.1 Sum 3. Print Program Output Enter first integer 45 Enter second integer 72 Sum is 117

2.3 Another Simple C Program:Adding Two Integers • As before • Comments, #include <stdio.h> and main • intinteger1,integer2,sum; • Declaration 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 • Declarations appear before executable statements • If an executable statement references and undeclared variable it will produce a syntax (compiler) error

2.3 Another Simple C Program: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

2.3 Another Simple C Program: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 %d\n",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 %d\n", integer1 + integer2 );

integer1 45 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 • A visual representation

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

2.5 Arithmetic • Arithmetic operators: • Rules of operator precedence:

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 structure • 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

2.6 Decision Making: Equality and Relational Operators

1 /* Fig. 2.13: fig02_13.c 2 Using if statements, relational 3 operators, and equality operators */ 4 #include <stdio.h> 5 6 int main() 7 { 8 int num1, num2; 9 10 printf( "Enter two integers, and I will tell you\n" ); 11 printf( "the relationships they satisfy: " ); 12 scanf( "%d%d", &num1, &num2 ); /* read two integers */ 13 14 if ( num1 == num2 ) 15 printf( "%d is equal to %d\n", num1, num2 ); 16 17 if ( num1 != num2 ) 18 printf( "%d is not equal to %d\n", num1, num2 ); 19 20 if ( num1 < num2 ) 21 printf( "%d is less than %d\n", num1, num2 ); 22 23 if ( num1 > num2 ) 24 printf( "%d is greater than %d\n", num1, num2 ); 25 26 if ( num1 <= num2 ) 27 printf( "%d is less than or equal to %d\n", 28 num1, num2 ); 1. Declare variables 2. Input 2.1 if statements 3. Print

29 30 if ( num1 >= num2 ) 31 printf( "%d is greater than or equal to %d\n", 32 num1, num2 ); 33 34 return 0; /* indicate program ended successfully */ 35 } 3.1 Exit main Program Output 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 Enter two integers, and I will tell you the relationships they satisfy: 22 12 22 is not equal to 12 22 is greater than 12 22 is greater than or equal to 12

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Chapter 3: Introduction to C Programming Language - PowerPoint PPT Presentation

Chapter 3: Introduction to C Programming Language

Chapter 3: introduction to c programming language c development environment a simple program example characters and tokens structure of a c program – powerpoint ppt presentation.

C development environment
A simple program example
Characters and tokens
Structure of a C program
comment and preprocessor directives
basic data types
data declarations
Basic functions
NOTE ABOUT C PROGRAMS
In C, lowercase and uppercase characters are very important! All commands in C must be lowercase. The C programs starting point is identified by the word
This informs the computer as to where the program actually starts. The brackets that follow the keyword main indicate that there are no arguments supplied to this program (this will be examined later on).
The two braces, and , signify the begin and end segments of the program.
Summary of major points so far
program execution begins at main()
keywords are written in lower-case
statements are terminated with a semi-colon
text strings are enclosed in double quotes
Characters are the basic building blocks in C program, equivalent to letters in English language
Includes every printable character on the standard English language keyboard except , and _at_
Example of characters
Numeric digits 0 - 9
Lowercase/uppercase letters a - z and A - Z
Space (blank)
Special characters , . ? / ( ) lt gt etc
A token is a language element that can be used in forming higher level language constructs
Equivalent to a word in English language
Several types of tokens can be used to build a higher level C language construct such as expressions and statements
There are 6 kinds of tokens in C
Reserved words (keywords)
Identifiers
String literals
Punctuators
Keywords that identify language entities such as statements, data types, language attributes, etc.
Have special meaning to the compiler, cannot be used as identifiers in our program.
Should be typed in lowercase.
Example const, double, int, main, void, while, for, else (etc..)
Words used to represent certain program entities (program variables, function names, etc).
int my_name
my_name is an identifier used as a program variable
void CalculateTotal(int value)
CalculateTotal is an identifier used as a function name
Entities that appear in the program code as fixed values.
4 types of constants
Integer constants
Positive or negative whole numbers with no fractional part
const int MAX_NUM 10
const int MIN_NUM -90
Floating-point constants
Positive or negative decimal numbers with an integer part, a decimal point and a fractional part
const double VAL 0.5877e2 (stands for 0.5877 x 102)
Character constants
A character enclosed in a single quotation mark
const char letter n
const char number 1
printf(c, S)
Output would be S
Enumeration
Values are given as a list
A sequence of any number of characters surrounded by double quotation marks.
My name is Salman
Example of usage in C program
printf(My room number is BN-1-012\n)
Output My room number is BN-1-012
Symbols used to separate different parts of the C program.
These punctuators include
Usage example
Tokens that result in some kind of computation or action when applied to variables or or other elements in an expression.
Example of operators
result total1 total2
Explanations or annotations that are included in a program for documentation and clarification purpose.
Completely ignored by the compiler during compilation and have no effect on program execution.
Starts with / and ends with /
Some compiler support comments starting with //
The first thing to be checked by the compiler.
Starts with .
Tell the compiler about specific options that it needs to be aware of during compilation.
There are a few compiler directives. But only 2 of them will be discussed here.
include ltstdio.hgt
Tell the compiler to include the file stdio.h during compilation
Anything in the header file is considered a part of the program
define VALUE 10
Tell the compiler to substitute the word VALUE with 10 during compilation
3 examples of basic data types
int (used to declare numeric program variables of integer type)
char (used to declare character variable)
double (used to declare floating point variable)
In addition, there are float, void, short, long, etc.
Declaration specifies the type of a variable.
Example int local_var
Definition assigning a value to the declared variable.
Example local_var 5
A variable can be declared globally or locally.
A globally declared variable can be accessed from all parts of the program.
A locally declared variable can only be accessed from inside the function in which the variable is declared.
A specification of an action to be taken by the computer as the program executes.
In the previous example, there are 2 lines following variable declaration and variable definition that terminate with semicolon .
global_var local_var VALUE
printf (Total sum is d\n, global_var)
Each line is a statement.
A C program consists of one or more functions that contain a group of statements which perform a specific task.
A C program must at least have one function the function main.
We can create our own function or use the functions that has been created in the library, in which case we have to include the appropriate header file (example stdio.h).
In this section, we will learn a few functions that are pre-defined in the header file stdio.h
These functions are
getchar() putchar()
In addition to those functions, we will also learn about Format Specifier and Escape Sequence which are used with printf() and scanf().
Used to send data to the standard output (usually the monitor) to be printed according to specific format.
General format
printf(control string, variables)
Control string is a combination of text, format specifier and escape sequence.
printf(Thank you)
d is a format specifier
\n is an escape sequence
Read data from the standard input device (usually keyboard) and store it in a variable.
scanf(Control string, variable)
The general format is pretty much the same as printf() except that it passes the address of the variable (notice the sign) instead of the variable itself to the second function argument.
getchar() - read a character from standard input
putchar() - write a character to standard output

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