Oop lec 1

Lecture No 1COMSATS Institute of Information

Technology

Review of Basic Programming Concepts

1 Object Oriented Programming

Basics of Typical C Program Development Environment

Object Oriented Programming2

A program development environmentThe languageC Standard Library

Six phases to be executed


EditPreprocessorCompileLinkLoadExecute

Stages of compilation


Preprocessing

Performed by a program called the preprocessor

Modifies the source code (in RAM) according to preprocessor directives (preprocessor commands) embedded in the source code

Strips comments and white space from the code


Compilation

Performed by a program called the compilerTranslates the preprocessor-modified source

code into object code (machine code)Checks for syntax errors and warnings

o If any compiler errors are received, no object code file will be generated.

o An object code file will be generated if only warnings, not errors, are received.


Linking

Combines the program object code with other object code to produce the executable file.

The other object code can come from the Run-Time Library, other libraries, or object files that you have created.

Saves the executable code to a disk fileo If any linker errors are received, no executable file

will be generated.

Simple c program


/* Filename: product.c Description: This program prompts the user for two integer values then displays

their product. */

#include <stdio.h>

int main( void )

{

int value1, value2, product ;

printf(“Enter two integer values: “) ;

scanf(“%d%d”, &value1, &value2) ;

product = value1 * value2 ;

printf(“Product = %d\n”, product) ;

return 0 ;

}

Anatomy of c program


program header comment

preprocessor directives (if any)

int main ( void ) { statement(s) return 0 ; }


A comment is descriptive text used to help a reader of the program understand its content.

Lines that begin with a # are called preprocessor directives (commands).

Every program must have a function called main. This is where program execution begins.

A left brace (curly bracket) -- { -- begins the body of every function. A corresponding right brace -- } -- ends the function body.


int value1, value2, product;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)value1, value2, productIdentifiers: consist of letters, digits (cannot begin with a

digit) and underscores( _ )Case sensitive

Declarations appear before executable statementsIf an executable statement references and undeclared

variable it will produce a syntax (compiler) error


scanf("%d%d", &value1,&value2);Obtains values from the user

scanf uses standard input (usually keyboard)This scanf statement has two arguments

%d - indicates data should be a decimal integer&value1 - location in memory to store variable

When executing the program the user responds to the scanf statement by typing in a number, then pressing the enter (return) key


= (assignment operator)Assigns a value to a variableIs a binary operator (has two operands)product = value1 * value2;

Variable receiving value on leftprintf( “Product is %d\n", product);

Similar to scanf%d means decimal integer will be printedproduct specifies what integer will be printed

Arithmetic


Arithmetic operators:

Rules of operator precedence:

C operation

Arithmetic operator

Algebraic expression

C expression

Addition + f + 7 f + 7

Subtraction - p – c p - c

Multiplication * bm b * m

Division / x / y x / y

Modulus % r mod s r % s

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.

*, /, or % Multiplication,Division, Modulus

Evaluated second. If there are several, they are evaluated left to right.

+ or - Addition Subtraction

Evaluated last. If there are several, they are evaluated left to right.

Decision Making: Equality and Relational Operators


Executable statementsPerform actions (calculations, input/output of data)Perform decisions

May want to print "pass" or "fail" given the value of a test grade

if control structureSimple version in this section, more detail laterIf 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 structureKeywords

Special words reserved for CCannot be used as identifiers or variable names

Decision Making: Equality and Relational Operators


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

not = != 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

Control Structures


Control Flow In C, three ways to specify sequence of statement executionSequential ExecutionConditional ExecutionIterative Execution

Conditional Execution


One-way selection or ifTwo-way selection or if-elseMultiple Selection or nested if

One-way selection or if


If(expression) statement1;If(x>10) y=z/x; y=z*x;If(x>y) printf(“the largest is %d”,x);

Two-way selection or if-else


If(expression) statement1; else statement2;If(x>y) printf(“the largest is %d”,x); else printf(“the largest is %d”,y);

Multiple Selection or nested if


If(condition1) { if(condition2) statement1; } else statement2;

Iterative Execution


The while statementThe for statementThe do-while statement

The while statement


While(expression) statement1;

#include<stdio.h>int main(){ Int k, num, maximum=10; k=1; while(k<=maximum) { scanf(“%d”, &num); printf(“%4d”, num); k++; }return 0;}

The for statement


for(expression1;expression2;expression3) statement1;expression1: initial valueexpression2: boolean expressionexpression3: update of expression

Example


#include<stdio.h>int main(){ int sum, n, i; sum = 0; scanf(“%d”, &n); for(i=1; i<=n; i++) sum = sum + i; printf(“Sum=%d\n”,sum); return 0;}

The do-while statement


do statement1 while(expression);

Example


#include<stdio.h>int main(){ int sum, num; sum = 0; num=1; do { sum = sum + num; num++; } while(num <= 10); printf(“Sum=%d\n”,sum); return 0;}

Other Control Structures


switchbreakcontinue

Example


#include<stdio.h>int main(){ int n; printf(“Enter an integer value\n” ); scanf(“%d”, &n); switch(n) { case 1: printf(“The value is 1\n”); break; case 2: printf(“The value is 2\n”); break; default: printf(“The value is neither 1 nor 2\n”); } return 0;}

Functions


An independent set of statements for performing some special tasks

AttributesName of function (user-defined)ParametersVariable declaration (if any)The body of function

Divisions of Function


Prototype int largest(int x, int y);

Definition Head function itself

Invocation large = largest (x, y);

Types of Function


System-supplied functionsTo instruct system to accomplish specific

operationsSaves programmers time to writing own functionsCompletely debugged, efficient and always

produce precise outputReduce source codeprintf(“%d”, x);

User-defined functionsDefined by programmer as part of source codeResult-type user-defined-name(parameters)

User-defined function


#include<stdio.h>int retlarge(int num1, int num2);int main(){ int num1, num2, large; scanf(“%d%d”, &num1, &num2) ; printf(“%d %d\n”, num1, num2) ; large = retlarge(num1, num2); printf(“large = %d\n”, large); return 0;}int retlarge(int x, int y){ if (x>y) return(x); else return(y);}

Methods for transmitting parameters


Passing by valuetreated as local variablesthe initial value is obtained by copying the

values of associated actual parametersPassing by location

passing by address or referencelinking actual parameters to formal

parameters by passing address of actual parameters from the calling program to called program

Arrays


Group of elements of same type. Collection of similar data type stored in contiguous memory location. To refer to an element, specify

Array namePosition number

Format:arrayname[ position number ]

First element at position 0n element array named c:

c[ 0 ], c[ 1 ]...c[ n – 1 ]

Name of array (Note that all elements of this array have the same name, c)

Position number of the element within array c

c[6]

-45

6

0

72

1543

-89

0

62

-3

1

6453

78

c[0]

c[1]

c[2]

c[3]

c[11]

c[10]

c[9]

c[8]

c[7]

c[5]

c[4]

Declaring Arrays


When declaring arrays, specifyNameType of arrayNumber of elementsarrayType arrayName[ numberOfElements ];

Examples:int c[ 10 ]; float myArray[ 3284 ];

Declaring multiple arrays of same typeExample:int b[ 100 ], x[ 27 ];


Initializersint n[ 5 ] = { 1, 2, 3, 4, 5 };

If not enough initializers, rightmost elements become 0

int n[ 5 ] = { 0 } All elements 0

If too many a syntax error is produced syntax error

C arrays have no bounds checkingIf size omitted, initializers determine it

int n[ ] = { 1, 2, 3, 4, 5 }; 5 initializers, therefore 5 element array


Character arraysString “first” is really a static array of charactersCharacter arrays can be initialized using string literals

char string1[] = "first"; Null character '\0' terminates strings string1 actually has 6 elements

It is equivalent tochar string1[] = { 'f', 'i', 'r', 's', 't', '\0' };Can access individual characters

string1[ 3 ] is character ‘s’Array name is address of array, so & not needed for

scanf scanf( "%s", string2 );

Reads characters until whitespace encountered Can write beyond end of array, be careful

Array Subscripting Formula


Address of i-th element = address of 0-th element + i * (size of type)

Assuming declaration int intarr[10];Assuming address of array intarr is located

at address 10 in memoryAccessing element intarr[5] can be

calculated by formula:Address of i-th element = 10 + 5 * 2 = 20

Pointers


Pointers are variables that contain memory addresses as their values.

A variable name directly references a value.

A pointer indirectly references a value. Referencing a value through a pointer is called indirection.

A pointer variable must be declared before it can be used.


Memory can be conceptualized as a linear set of data locations.

Variables reference the contents of a locationsPointers have a value of the address of a given

locationA declaration int intval=10;

Then int ptr can be set as int *ptr;Pointing to intval by ptr = &intval;Address of intval assigned to ptr, not contents!

& and *


When is & used?

When is * used?

& -- "address operator" which gives or produces the memory address of a data variable

* -- "dereferencing operator" which provides the contents in the memory location specified by a pointer

Pointers and Function


Pointers can be used to pass addresses of variables to called functions, thus allowing the called function to alter the values stored there.

If instead of passing the values of the variables to the called function, we pass their addresses, so that the called function can change the values stored in the calling routine. This is known as "call by reference" since we are referencing the variables.

Passing pointers to function


#include <stdio.h>

void exchange ( int *a, int *b ) ;

int main ( )

{

int a = 5, b = 6;

printf("a=%d b=%d\n",a,b) ;

exchange (&a, &b) ;

printf("a=%d b=%d\n",a,b) ;

return 0 ;

}


void exchange( int *a, int *b )

{

int temp;

temp= *a; *a= *b; *b = temp ;

printf ("a=%d b=%d\n", *a, *b);

}

Results:

a=5 b=6

a=6 b=5

a=6 b=5

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