Introduction to C Language Day 2

8/8/2019 Introduction to C Language Day 2

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Introduction to C LanguageIntroduction to C Language

Day 2

by Supreet Singh


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Arrays

Arrays


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ArraysArrays

An array is a series of variables, all being sametype and size

Each variable in an array is called an array

element All the elements are of same type, but may contain

different values

The entire array is contiguously stored in memory

The position of each array element is known asarray index or subscript

An array can either be one dimensional (1-D) ortwo dimensional (2-D) or Multi-dimensional


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Declaring a 1Declaring a 1--D ArrayD Array

Syntax:

data-type arrayname[size];

Example:

int aiEmployeeNumbers[6];float afSalary[6];

The array index starts with zero

The valid array indexes for the above declared array is 0 to 5

When an array is declared inside a function without initializing it, the elementshave unknown (garbage) values and outside the function the elements have

zero/default values


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Declaring and Initializing arrays (1 of 2)Declaring and Initializing arrays (1 of 2)

Arrays can be initialized as they are declared

Example:

int aiEmployeeNumbers[] = {15090, 15091, 15092,

15093,15094, 15095};

The size in the above case is optional and it isautomatically computed

In the above example size of the array is 6 and itoccupies 6 * 4 = 24 bytes (6 is the size of the array and4 is the number of bytes required to store one integeron Windows platform)


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Declaring and Initializing 1Declaring and Initializing 1--D arrays (2 ofD arrays (2 of

2)2)

When an array is partially initialized within afunction the remaining elements will begarbage values and outside any function the

remaining elements will be zero valuesExample:

int aiEmployeeNumbers[6] ={15090, 15091, 15092};

In the above example, the array indexes from3 to 5 may contain zero or garbage values


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22--D ArraysD Arrays

A 2-D array is used to store tabular data in terms of rows andcolumns

A 2-D array should be declared by specifying the row size and thecolumn size

To access the individual elements, the row and the column should besupplied

The 2-D array is essentially a one dimensional array wherein eachelement itself is another array, hence an array of arrays

As far storage is concerned, the row elements are in continuouslocations of memory hence called row major ordering in C language

The table type visualization of rows and columns is therefore only forconvenience


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Declaring and using 2Declaring and using 2--D ArraysD Arrays

A 2-D array can be declared by specifying the maximum size for rows andcolumns

Syntax:data type arrayname [Row Size][Column Size];

Example:

int aiEmployeeInfo[3][2];The above declaration declares aiEmployeeInfo with 3 rows and 2 columns

To access the individual elements row index (starts from zero) and thecorresponding column index (starts from zero) should be supplied

Example:printf(%d,aiEmployeeInfo[0][1]);

The above printf references the information at 0th row 1st column


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Initializing 2Initializing 2--D Arrays(1 of 2)D Arrays(1 of 2)

A 2-D array can be initialized as given below:

int aiEmployeeInfo[3][2]= {101,1,102,1,103,2};

In the above declaration,101, 102 and 103 refers to employeeids and they are stored

in [0][0], [1][0] and [2][0] positions1,1 and 2 refers to Job Codes and they are stored in [0][1],

[1][1] and [2][1] positions


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Initializing 2Initializing 2--D Arrays (2 of 2)D Arrays (2 of 2)

A 2-D array can be declared without specifying the row size ifit is initialized

Example:

int aiEmployeeInfo[][3]= {101,1,102,1,103,2};Since there are six initial values and the column size is 3, the

number of

rows is taken as 2

If the column size is not supplied then there will be a

compilation error


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Pointers


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Pointers(1 of 5)Pointers(1 of 5)

A pointer is a special variable which stores theaddress of a memory location. It can be theaddress of a variable or directly the address of alocation in memory

A variable is a name given to a set of memorylocations allocated to it

For every variable there is an address, which is the

starting address of its set of memory locations

If a variable called p holds the address of anothervariable i then p is called as a pointer variableand p is said to point to i


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PointersPointers --Address of Operator(2 of 5)Address of Operator(2 of 5)

Ampersand (&) is the address of operator .It is used to fetch the

memory address of a variable

* is called the indirection operator, dereferencing or value at address

operator and is used with a pointer variable to fetch the value at a

given memory location Both these operators are used with pointers


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PointersPointers -- Address of Operator(3 of 5)Address of Operator(3 of 5)

To print the address of a variable, precede the variable with an

ampersand (&)

Example:

int iNumber = 100;

printf(The value is %d\n,iNumber);

printf(The address is %u\n,&iNumber);

printf(The address in hexa decimal is

%x\n,&iNumber);

Since an address is an unsigned

integer, %u is used as a conversion

specifier

An address can be printed in hexa

decimal form using %x as the conversion

specifier


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To declare a pointer variable, use the following syntaxdata-type *pointerName;

Example:

1. int *piCount;This declaration tells the compiler that piCount will beused to store the address of an integer value in other words piCount points to an integer variable.

2. float *pfBasic;

This statement declares pfBasic as a pointer variablewhich can contain the address of a float variable.

Note: The size of pointer variable on Windows platform is 4 bytes.

However it may vary from one platform to another.


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Example:

int iCount = 8;

int *piCount;

piCount = &iCount;

printf(Value=%d,*piCount);

iCount: an integer variable

piCount: an integer pointer &: the address of operator

* : the indirection operator


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Reading Contents of a variable usingReading Contents of a variable using

PointersPointers

To access the value at the address stored in the pointer, usethe following syntax *pointervariable

Example:printf(%d, *piCount);

y

Here the*

operator preceding piCount will fetch the value at theaddress stored in piCount

Using == operator (Equal to) on pointers, will check whetherboth pointers being compared are pointing to the sameaddress or not

Uninitialized pointers may point to any memory location

Using * (indirection operator) on uninitialized pointers mayresult in program throwing a run time error


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NULL PointersNULL Pointers

Using a pointer without initializing it to anyvalid address may result in data corruption oreven program crash

To differentiate between initialized and uninitialized pointers, we usually set an uninitialized pointer to NULL

Example:

/* Initializing pointer to NULL */

int *piCount = NULL;


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StringsStrings


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Strings (1 of 2)Strings (1 of 2)

A string is a series of characters in a groupthat occupy contiguous memory

Example:

CDAC

Information Technology

A string should always be enclosed with indouble quotes ()


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Strings (2 of 2)Strings (2 of 2)

In memory, a string ends with a nullcharacter\0

Space should be allocated to store \0 aspart of the string

A null character (\0) occupies 1 byte ofmemory


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Declaration of Strings (1 of 2)Declaration of Strings (1 of 2)

Syntax:char variablename [Number_of_characters];

Example:char acEmployeeName[20];

Here 20 implies that the maximum number of characters can be 19and one position is reserved for \0

Since a character occupies one byte, the above array occupies 20bytes (19 bytes for the employee name and one byte for \0)


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Declaration of Strings (2 of 2)Declaration of Strings (2 of 2)

/* Declare String as a char pointer */

char *pcName = Cdac;

/* Declaring a string as a character array */char acName[ ] = Cdac;

Think why \0 requires only one byte!!


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Printing Strings to Console (1 of 2)Printing Strings to Console (1 of 2)

Using Character pointer:

char *pcProg = C Fundamentals;printf(pcProg);

printf(This is %s course,pcProg);

Using CharacterArray:

char acProg[] = C Fundamentals;printf(acProg);

OR

printf(%s, acProg );printf(This is %s course,acProg);


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Printing Strings to Console (2 of 2)Printing Strings to Console (2 of 2)

Printing a string as part of a formattedstring

int iCourseId = 27;char *pcProg = C Fundamentals;

/* print the courseId (Int)and Course name(char*) */

printf(The Id of this courseis %d and this course is %s

\n,iCourseId, pcProg);


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strlen() Functionstrlen() Function

strlen() function is used to count the number of characters in the string

Counts all the characters excluding the null character \0

Syntax:

unsigned int strlen (char string[]);Here string[ ] can be a string constant or a character pointer or a character

array and the function returns unsigned int

Example:

strlen(Programming Fundamentals);returns 24

strlen(acItemCategory); returns the number of characters inthe

character array acItemCategory


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Input of StringsInput of Strings scanf and gets functionsscanf and gets functions

scanf(%s, acItemCategory);

scanf(%s, &acItemCategory[0]);

Both the input functions are valid. The first one passes the base

address (Address of the first element) implicitly

The second function passes the address of the first element explicitly

gets(acItemCategory);

gets(&acItemCategory[0]);

This is an unformatted function to read strings


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String Handling functionsString Handling functions

The following are the string functions that aresupported by C

strlen() strcpy() strcat()strcmp() strcmpi() strncpy()

strncat() strncmp()strnicmp()

These functions are defined in string.h header file

All these functions take either a character pointer or acharacter array as an argument


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strcpy() Functionstrcpy() Function

strcpy() function is used to copy one string to another

Syntax:

strcpy (Dest_String , Source_String);

y Here Dest_string should always be variable

y Source_String can be a variable or a string constant

y The previous contents of Dest_String, if any, will be over written

Example:

char acCourseName[40];

strcpy(acCourseName , C Programming);

The resultant string in acCourseName will be C Programming


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strcat() Functionstrcat() Function

strcat() function is used to concatenate (Combine) two strings

Syntaxstrcat( Dest_String_Variable , Source_String ) ;

In this, the Destination should be a variable and Source_String can

either be a string constant or a variable.The contents of Dest_String is concatenated with Source_Stringcontents and the resultant string is stored into Dest_String variable.

Example:char acTraineeFpCourse [50] = The course is ;strcat(acTraineeFpCourse,Oracle 10G);

The resultant string in acTraineeFPCourse will be The course isOracle 10G


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strcmp() Function (1 of 2)strcmp() Function (1 of 2)

strcmp() function is used to compare twostrings

strcmp() does a case sensitive (Upper caseand lower case alphabets are considered tobe different) comparison on strings

Syntax:int strcmp( String1 , String2);Here both String1 and String2 can either be a variable or a string

constant


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strcmp() Function (2 of 2)strcmp() Function (2 of 2)

strcmp() function returns an integer value

If strings are equal, it returns zero

If the first string is alphabetically greater than thesecond string then, it returns a positive value

If the first string is alphabetically less than the second

string then, it returns a negative value

Example:

strcmp(My Work, My Job); returns apositive value


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strcmpi() Functionstrcmpi() Function

strcmpi() function is same as strcmp()

function but it is case insensitive

Example:strcmpi(My WoRk , MY work); returns zero


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FunctionsFunctions


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FunctionsFunctions

A function is a section of a program that performs a specific task

Function groups a number of program statements into a unit and

gives it a name. This unit can be reused wherever it is required in

the program

Functions employ the top down approachand hence becomes

easier to develop and manage

main()

FunctionFunctionFunction

callcallcall

User defined function


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Advantages ofFunctionsAdvantages ofFunctions

The functions can be developed by different people and canbe combined together as one application

Solving a problem using different functions makesprogramming much simpler with fewer defects

Easy to code,modify,debug and also to understand the code

Functions support reusability ie. once a function is written itcan be called from any other module without having to rewrite

the same. This saves time in rewriting the same code


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Passing values to functions and returningPassing values to functions and returning

valuesvalues

Functions are used to perform a specific task on a set of values

Values can be passed to functions so that the function performs thetask on these values

Values passed to the function are called arguments

After the function performs the task, it may send back the results tothe calling function

The value sent back by the function is called return value

A function can return back only one value to the calling functionthrough a return statement

Function may be called either from within main() or from withinanother function


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Elements of a FunctionElements of a Function

Function Declaration orFunction Prototype :

The function should be declared prior to its usage

Function Definition :

Implementing the function or writing the task of the function

Consists of

Function Header

Function Body

Function Invocation orFunction call:

To utilize a functions service, the function have to be invoked

(called)


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Declaring Function Prototypes (1 of 2)Declaring Function Prototypes (1 of 2)

A function prototype is the information to the compilerregarding the user-defined function name, the datatype and the number of values to be passed to thefunction and the return data type from the function

This is required because the user-defined function iswritten towards the end of the program and the maindoes not have any information regarding thesefunctions

The function prototypes are generally written beforemain. A function prototype should end with asemicolon


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Declaring Function Prototypes (2 of 2)Declaring Function Prototypes (2 of 2)

Function Prototypes declare ONLY the signature of the function beforeactually defining the function

Here signature includes function name, return type, list of parameter datatypes and optional names of formal parameters

Syntax:Return_data_type FunctionName (data_type arg1,

data_type arg2,...,data_type argn );

Example:

int fnValidateDate(int iDay,int iMonth, int iYear);

In the above example, iDay, iMonth and iYear are optional. Thesame can also be written as:

int fnValidateDate(int,int, int);


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Writing UserWriting User--Defined FunctionsDefined Functions

A function header and body looks like this:Return-data-type function-name(data-type argument-1,

data-type argument-2,.){

/* Local variable declarations *//* Write the body of the function here */

Statement(s);return (expression);

}

The return data type can be any valid data type

If a function does not return anything then the voidis the return type

A function header does not end with a semicolon

The return statement is optional. It is required only when a valuehas to be returned


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Writing UserWriting User--Defined FunctionsDefined Functions

int fnAdd(int iNumber1, int iNumber2){

/* Variable declaration*/

int iSum;

/* Find the sum */

iSum = iNumber1 + iNumber2;

/* Return the result */

return (iSum);

}

Return data type Arguments

(Parameters)

Function

header

Function Body

Can also be written as return iSu


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Returning valuesReturning values

The result of the function can be given back to the calling functions

return statement is used to return a value to the calling function

Syntax:return (expression) ;

Example:

return(iNumber * iNumber);return 0;

return (3);return;

return (10 * iNumber);


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Calling UserCalling User--Defined Functions (1 of 2)Defined Functions (1 of 2)

A function is called by giving its name and passing therequired arguments

The constants can be sent as arguments to functions

/* Function is called here */iResult = fnAdd(10, 15);

The variables can also be sent as arguments tofunctions

int iResult,iNumber1=10, iNumber2=20;

/* Function is called here */

iResult = fnAdd(iNumber1, iNumber2);


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Calling UserCalling User--Defined Functions (2 of 2)Defined Functions (2 of 2)

Calling a function which does not returnany value

/* Calling a function */

fnDisplayPattern(15);

Calling a function that do not take any

arguments and do not return anything/* Calling a function */

fnCompanyNameDisplay();


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Function TerminologiesFunction Terminologies

void fnDisplay() ;

int main(int argc, char **argv){

fnDisplay();

return 0;

}

void fnDisplay(){

printf(Hello World);

}

Function Prototype

Calling

Function

Function Call Statement

Function

Definition

Called Function


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Formal and Actual ParametersFormal and Actual Parameters

The variables declared in the functionheader are called as formal parameters

The variables or constants that arepassed in the function call are called asactual parameters

The formal parameter names and actualparameters names can be the same ordifferent


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FunctionsFunctions Example (1 of 2)Example (1 of 2)

int fnAdd(int iNumber1, int iNumber2);

int main(int argc, char **argv) {

int iResult,iValue1=5, iValue2=10;

/* Function is called here */

iResult = fnAdd(iValue1, iValue2);

printf(Sum of %d and %d is %d\n,iValue1,iValue2,iResult);

return 0;

}

Function Prototype

Actual Arguments


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FunctionsFunctions Example (2 of 2)Example (2 of 2)

/* Function to add two integers */

int fnAdd(int iNumber1, int iNumber2){

/* Local variable declaration*/

int iSum;

iSum = iNumber1 + iNumber2; /* Find the sum */

return (iSum); /* Return the result */

}

Formal Arguments

Return value


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ParameterPassing TechniquesParameterPassing Techniques

When a function is called and if the

function accepts some parameters, then

there are two ways by which the function

can receive parameters

Pass by value

Pass by reference


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Pass by Value (1 of 3)Pass by Value (1 of 3)

When parameters are passed from thecalled function to a calling function, thevalue of the actual argument is copied

onto the formal argument

Since the actual parameters and formal

parameters are stored in different memorylocations, the changes in formalparameters do not alter the values ofactual parameters


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void fnUpdateValues(int iNumber1, int iNumber2);

int main(int argc, char **argv) {int iValue1=100, iValue2=250;printf("\n\nBefore calling the function: ");

printf("ivalue1=%d iValue2=%d\n\n",iValue1,iValue2);

/* Call the function */

fnUpdateValues(iValue1, iValue2);

printf("After calling the function: ");

printf(" ivalue1=%d iValue2=%d\n\n",iValue1,iValue2);

return 0;}void fnUpdateValues(int iNumber1, int iNumber2){

/* Update the values */

iNumber1 = iNumber1 + 15;

iNumber2 = iNumber2 - 10;}


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main()

100

200

fnUpdateValues()

115

240

End of function fnUpdateValues


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Pass by Reference (1 of 4)Pass by Reference (1 of 4)

Addresses of actual parameters arepassed

The function should receive the addressesof the actual parameters through pointers

The actual parameters and formalparameters if referencing the samememory location, then the changes thatare made become permanent


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Pass By Reference (2 of 4)Pass By Reference (2 of 4)

void fnUpdateValues(int *piNumber1, int *piNumber2);

int main(int argc, char **argv){

int iValue1=100, iValue2=250;printf("\n\nBefore calling the function: ");

printf("ivalue1=%diValue2=%d\n\n",iValue1,iValue2);

/* Call the function and send the address of thevariables */

fnUpdateValues(&iValue1, &iValue2);

printf("After calling the function: ");

printf("ivalue1=%diValue2=%d\n\n",iValue1,iValue2);return 0;

}


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Pass By Reference (3 of 4)Pass By Reference (3 of 4)

void fnUpdateValues(int

*piNumber1, int *piNumber2){

*piNumber1 = *piNumber1 + 15;

*piNumber2 = *piNumber2 - 10;

}


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Pass by Reference (4of 4)Pass by Reference (4of 4)

amain()

115

240

fnUpdateValues()

Address of

iValue1

Address of

iValue2

End of function fnUpdateValues


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QUESTIONS?QUESTIONS?


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THANK YOU.THANK YOU.

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Introduction to C Language Day 2