Lk module3

Programming in C & Data Structures: 15PCD13/23
Compiled & Edited by: Prof. L. Krishnananda, HOD, Dept of ECE, Govt SKSJTI, Bengaluru Page 1
1) Arrays in C:
 A normal variable can hold only one value.
 Sometime it is required to use a single name for group of data items.
 Such a construct of programming language which stores and organizes a set of data item is called
data structure.
 Different types of data structure are arrays, stacks, queues, linked lists, structures, trees and files etc.
 An array can be defined as an ordered list of homogenous data elements.
 May be of type int, float, char or double.
 All these elements are stored in consecutive memory locations.
 An array is described by a single name or an identifier and each element in an array is referenced by a
subscript (or an index) enclosed in a pair of square brackets.
 For array, memory allocated is static. i.e., if array size is changed during the program execution, it may
result in garbage value or memory overflow condition.
 Array must be declared before it appears in C Program
 Arrays are classified into two types:
o One-dimensional
o Multi-dimensional
 The dimensionality of an array is determined by the number of subscript present in the given
array. i.e., the number of brackets written after the array name.

 If there is only one subscript, then it is called a one-dimensional array.
 If the number of subscripts is more than one, then such arrays are called multi-dimensional arrays.
 Dimension is determined by the number of pairs of square
 brackets placed after the array name.
 Example:
 array1[ ] -> One-Dimensional Array
 array2[ ][ ] -> Two-dimensional Array
 array3[ ] [ ] [ ] -> Three-dimensional Array
You can also declare an array without explicitly indicating the size. Compiler will decide & allocate memory
accordingly. int array[ ] = { 100, 200, 300, 400};
Example program:
#include <stdio.h>
#define MONTHS 12
void main( )
{
int days[ ]= {31,28,31,30,31,30,31,31,30,31,30,31};
int index;
for (index = 0; index < MONTHS; index++)
printf("Month %d has %2d days.n", index +1, days[index]);
}
/* Program to read marks of students and display using Array*/

/* Program to count the no of positive, negative numbers and zeros in an array*/
#include <stdio.h>
#include <conio.h>
void main( )
{
int a[50],n, count_neg=0,count_pos=0, count_zero=0; k;
printf(“Enter the size of the arrayn”);
scanf(“%d”,&n);
printf(“Enter the elements of the arrayn”);
for(k=0;k < n;k++)
scanf(“%d”,&a[k]); // reading elements of the array
for(k=0;k < n;k++) // to count positive, negative numbers and zeros
{
if(a[k] < 0)
count_neg++;
else if ( a[k]>0)
count_pos++;
else
count_zero++;
}
printf(“There are %d negative numbers in the arrayn”, count_neg);
printf(“There are %d positive numbers in the arrayn”, count_pos);
getch( );
}

Searching techniques:
finding the location of given element.
two approaches to search:
•Linear Search
•Binary Search
Linear Search: (Sequential Search)
–Sequentially scan the array, comparing each array item with the searched value one by one.
–If a match is found; return the location of the matched element; otherwise return –1

Another program for Linear Search:
Binary Search
value
•If equal, match found
•If key < middle, looks in first half of array
•If key > middle, looks in last half
•Repeat
n
> number of elements
•Ex: 30 element array takes at most 5 steps ,i.e., 25
> 30, so at most 5 steps

/* Binary Search C program*/
Sorting Techniques: Bubble sort, Insertion Sort, Selection Sort, Quick sort, Radix sort
etc

Two Dimensional Array:

Ex: The following initializes a 2-d array named X[4][3]:
int X[4] [3] = { {1, 2, 3} , { 4, 5, 6} , {7, 8, 9} , {10, 11, 12} };
Also can be written as:
int X[4] [3] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
– is equivalent to
X[0][0] = 1; // element at 0th
row & 0th
column
X[0][1] = 2;
X[0][2] = 3;
X[1][0] = 4; // element at 1st
row & 0th
column
...
X[3][2] = 12
Declaring 2-d arrays:

Matrix Multiplication program in C:

2) Strings in C:
 Strings in C are simply arrays of characters.
o Example: char s [10];
 This is a ten (10) element array that can hold a character string consisting of  9 characters.
 This is because C does not know where the end of an array is at run time.
o By convention, C uses a NULL character '0' to terminate all strings in its library
functions
 For example:
o char str [10] = {'u', 'n', 'I', 'x', '0'};
 It’s the string terminator (not the size of the array) that determines the length of the string.
 The first element of any array in C is at index 0. The second is at index 1, and so on ...
Example declaration:
char s[10];
s[0] = 'h'; s[1] = 'e’; s[2] = 'l'; s[3] = 'l'; s[4] = 'o’; s[5] = '0';
Initializing char array:
– char s[10] ="unix"; /* s[4] is '0'; */
– char s[ ] ="unix"; /* s has 5 elements; array size not indicated*/

A string can be read in or written out using the input/output statements.
Reading string
 scanf() with the %s format specification.
 gets() function
 getchar() function several times.
Writing string
 printf() with the %s format specification.
 puts() function
 putchar() function several times

1) Printing a string literal with printf ():
char msg[ ] = "A message to display";
printf ("%sn", msg);
printf expects to receive a string as an additional parameter when it sees %s in the format string
printf knows how much to print out because of the NULL character at the end of all strings.
– When it finds a 0, it knows to stop.
2) printing using puts ()
The puts function is a much simpler output function than printf for string printing.
Prototype of puts is defined in stdio.h
int puts(const char * str)
– This is more efficient than printf, because your program doesn't need to analyze the
format string at run-time.
For example:
char name[ ] = "The world of programming n";
puts (name);
Output on the screen:
The world of programming
3) Reading a string using scanf function
To read a string include:
– %s scans up to but not including the “next” white space character
– %ns scans the next n characters or up to the next white space character, whichever
comes first
Example:
scanf ("%s%s%s", s1, s2, s3);
scanf ("%2s%2s%2s", s1, s2, s3);
– Note: No ampersand(&) with scanf when inputting strings into character arrays!
4) Reading a string using gets
gets( ) gets a line from the standard input.
The prototype is defined in stdio.h
char *gets(char *str)
– str is a pointer to the space where gets will store the line to, or a character array.
– Returns NULL upon failure. Otherwise, it returns str.
char city[100];
printf("Enter a line:n");
gets(city);
puts("Your input is:n");
puts(city);
Difference between gets and scanf (“%s”):
gets reads an entire line from standard input. But scanf only reads what you tell it to. i..e, you told
scanf to read just a single %s, which means just a group of non-whitespace characters. So, it quits
reading from input, when it encounters the first white-space character.
– gets () reads an entire line of text from the keyboard
– scanf("%s",…) reads until the next whitespace character
Difference between puts and printf (“%s”):
puts() can be preferred for printing a string because it is generally less expensive (implementation of
puts() is generally simpler), and if the string has formatting characters like ‘%’, then printf() would
give unexpected results. Also, if str is a user input string, then use of printf() might cause security
issues. Also note that puts() moves the cursor to next line, i.e., automatically appends a new line after
printing.

Example Programs on Strings:
/* Example program on strings using for loop */
#include<stdio.h>
#include<conio.h>
void main()
{
char a[ ]="ECE DEPARTMENT";
int i=0;
clrscr( );
for(i=0;i<=15;i++)
{
printf("%c",a[i]);
} // end of for loop
getch( );
}
/* Example program on strings using while loop */
#include<stdio.h>
#include<conio.h>
void main()
{
char a[30]="ECE DEPARTMENT";
int i=0;
clrscr( );
while(a[i]!='0')
{
printf("%c",a[i]);
i++;
} // end of while loop
getch( );
}
/* Example prog using printf (“%s”) function */
#include<stdio.h>
#include<conio.h>
void main()
{
char a[ ]="CIVIL DEPARTMENT";
clrscr();
printf("%s",a);
getch();
}
/* Example prog using puts function */
#include<stdio.h>
#include<conio.h>
void main()
{
char a[ ]="CIVIL DEPARTMENT";
clrscr ( );
puts (a);
getch();
}

/* program to find and count the occurrence of characters in a string */
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char text[25]="c programming is good";
int i, m=0,p=0,r=0;
clrscr();
for(i=0;i<=25;i++)
{
if(text[i]=='m')
++m;
if(text[i]=='r')
++r;
if(text[i]=='o')
++p;
}
printf("n'm' found in text = %d times",m);
printf("n'r' found in text = %d times",r);
printf("n'o' found in text = %d times",p);
getch();
}
C Supports a number of string handling functions.
Header File - string.h
Standard Library functions in string.h header file:
S.no String functions Description
1 strcat (s1, s2 ) Concatenates s2 at the end of s1 and returns s1. (s1 is now s1+s2)
2 strncat (s1, s2, n ) appends n characters of string s2 to string s1 and returns s1.
3 strcpy (s1, s2 ) Copies s2 into s1 and returns s1. i.e., s1 is replaced by s2.
4 strncpy (s1,s2,n ) copies n characters from s2 to s1. Returns s1.
5 strlen (str) gives the length of str, not counting the NULL character.
6 strcmp (s1,s2 )
Compares S1 and S2 for equality.(ASCII values are compared) Returns 0 if
s1 is same as s2, positive value if s1>s2, negative value if s1<s2

7 strcmpi ( )
Same as strcmp() function. But, this function neglects the case of the
character. “A” and “a” are treated as same.
8 strchr ( s1) Returns pointer to first occurrence of char in s1.
9 strrchr ( ) last occurrence of given character in a string is found
10 strstr ( ) Returns pointer to first occurrence of str2 in str1.
11 strrstr ( ) Returns pointer to last occurrence of str2 in str1.
12 strdup ( ) duplicates the string
13 strlwr ( ) converts string to lowercase
14 strupr ( ) converts string to uppercase
15 strrev ( ) reverses the given string
16 strset ( ) sets all character in a string to given character
17 strnset ( ) It sets the portion of characters in a string to given character
18 strtok ( ) tokenizing given string using delimiter
Some of the string handling functions are:
1) strcmp()- function
The function compares two strings character by character and return one of the three values: -1,0,1
C strings can be compared for equality or inequality. If they are equal - they are ASCII identical.
If they are unequal, the comparison function will return an int that is interpreted as:
< 0 : str1 is less than str2
0: str1 is equal to str2
> 0: str1 is greater than str2
Syntax:
a) int strcmp (char *str1, char *str2) ;
Does an ASCII comparison one char at a time until a difference is found between two chars
Return value is as stated before
If both strings reach a '0' at the same time, they are considered equal.
b) int strncmp (char *str1, char * str2, size_t n);
Compares n chars of str1 and str2
– Continues until n chars are compared or the end of str1or str2 is encountered
Also have strcasecmp() and strncasecmp() which do the same as above, but ignore case in letters.
2) strcpy()- function
 The function used to copy one string to the other.
 Syntax - strcpy(string1,string2)
 The Content on string1 will be overwritten by content of string2.
3) strcat()- function
 The function used to concatenate.
 Syntax - strcat(string1,string2)
 String string2 is appended to the end of string1.
4) strlen()- function
 The function returns the numbers of characters in the string. The string length does not include
the ’0’(null) character.
 Syntax - strlen(string1)
 string1 is one dimension array of characters.
5) strncmp()- function

 The function used to compare the first n character of string.
 Syntax - strncmp(string1,string2,n)
 -1 - if ASCII value of the charecter of first string is less than of the second.
 0 - if both strings are same
 1 - if both strings are different
6) strlwr()- function
 The function is used to convert any uppercase letters in a string to its equivalent lowercase.
 Syntax - strlwr(string1)
 string1 is one dimension array of characters.
7) strncat()- function
 The function used to append first n characters of the second string at the end of the first string.
 Syntax - strncat(string1,string2,n)
8) strchr()- function
 The function seraches for for specified character in a given string.
 Returns NULL if the desired character is not found in the string.
 Syntax - strncat(string, desired-char)
/* illustration of strlen() Library function */
#include<stdio.h>
#include<conio.h>
void main()
{
char text[20];
int length;
clrscr();
printf("Type the Text n");
gets(text);
length=strlen(text);
printf("Length of string = %d", length);
getch();
}
/* illustration of strcpy() Library function */
#include<stdio.h>
#include<conio.h>
void main()
{
char str1[20], str2[20];
int length;
clrscr();
printf("Enter 1st stringn");
gets(str1);
printf("Enter 2nd stringn");
gets(str2);
printf("n1st String is --->t%s",str1);
printf("n2nd String is --->t%s",str2);
strcpy(str1,str2);
printf("nn1st String after strcpy() is --->t%s",str1);
getch();
}

/* illustration of strcmp() Library function */
#include<stdio.h>
#include<conio.h>
void main()
{
int result;
clrscr();
gets(str1);
gets(str2);
result=strcmp(str1,str2);
//In case of match result will be ZERO otherwise NON ZERO
printf("nnResult after Comparing is %d",result);
if (result==0)
printf (“n strings are same n”);
else
printf (“ strings %s and %s are differentn”, str1, str2);
getch();
}
/* illustration of strcat() Library function */
#include<stdio.h>
#include<conio.h>
void main()
{
char str1[20],str2[20];
int length;
clrscr();
gets(str1);
gets(str2);
strcat(str1,str2);
printf("nnString after strcat() is --->t%s",str1);
getch();
}
/* illustration of strrev() Library function */
#include<stdio.h>
#include<conio.h>
void main()
{
int length;
clrscr();
gets(str1);

str2 = strrev(str1);
printf("nnString after strrev() is --->t%s",str2);
if (str2==str1)
printf (“n given string %s is palindrome”, str1);
else
printf (“n given string %s is not palindrome”, str1);
getch();
}
/* Program to check for string palindrome without using strrev()*/
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char str[10];
int i=0,j,test;
clrscr();
printf("Enter the word t");
gets(str);
j=strlen(str)-1;
while(i<=j)
{
if(str[i]==str[j])
test=1;
else
{
test=0;
break;
}
i++;
j--;
} // end of while
if(test==1)
printf("nword %s is palindrome", str);
else
printf("n word %s is not palindrome", str);
getch();
}
/* program to count the number of words in a sentence */
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char text[30];
int count=0,i=0;
clrscr();
printf("Enter the line of textn");
printf("Give one space after each wordn");
gets(text);
while(text[i++]!='0')
{

if (text[i]==32 || text[i]=='0')
count++;
}
printf("Number of words in line = %d",count);
getch();
}
/* program to illustrate strcpy and strcat */
#include <string.h>
#include <stdio.h>
int main() {
char str1[27] = "abc";
char str2[100];
printf("%dn",strlen(str1));
strcpy(str2,str1);
puts(str2);
puts("n");
strcat(str2,str1);
puts(str2);
getch();
}
/* program to find the occurrence of a character in a string literal */
/* Searching Strings
Example use of strchr: */
#include<stdio.h>
#include<string.h>
int main() {
char ch='b', buf[80];
strcpy(buf, "The quick brown fox");
if (strchr(buf,ch) == NULL)
printf ("The character %c was not found.n",ch);
else
printf ("The character %c was found at position %dn", ch, strchr(buf,ch)-buf+1);
}

/* Palindrome program using library function in string.h */

/* String Palindrome Program using Pointers */
/* String reverse using Pointers */

Converting Strings to Numbers:
Contained in <stdlib.h> and are often used
int atoi (char *ptr);
– Takes a character string and converts it to an integer.
– White space and + or - are OK.
– Starts at beginning and continues until something non-convertible is encountered.
Some examples:
String Value returned
"157" 157
"-1.6" -1
"+50x" 50
"twelve" 0
"x506" 0
long atol (char *ptr) ;
– Same as atoi except it returns a long.
double atof (char * str);
– Handles digits 0-9.
– A decimal point.
– An exponent indicator (e or E).
– If no characters are convertible a 0 is returned.
Examples:
– String Value returned
"12" 12.000000
"-0.123" -0.123000
"123E+3" 123000.000000
"123.1e-5" 0.001231

3) Functions in C:
De_nition
 A Function is a self-contained block of statement that perform a coherent task of some kind.
 Every C Program can be thought of as a collection of these functions.
 Function is a set of instruction to carryout a particular task.
 Function after its execution may/may not return a value.
 Generally, the function are classified into standard function and user-defined functions.
 The Standard function are also called library function or built-in function.
 All standard functions, such as sqrt(), abs(), log(), sin(), printf() etc. are provided in the library
of function.
 But, most of the application need other functions than those available in the library; these are
known as user-defined functions.
 A function receives zero or more parameters from the calling program, performs a specific
task, and returns zero or one value.
 A function is invoked by its name and parameters.
o No two functions can have the same name in your C program.
o The communication between the function and invoker is through the parameters and the
return value.
 A function is independent:
o It is “completely” self-contained.
o It can be called at any places of your code and can be ported to another program.
 Functions make programs reusable and readable
Advantages of Modular Programming using Functions:
 Reduction in code redundancy
 Enabling code reuse
 Better readability
 Information Hiding
 Improved debugging and testing
 Improved maintainability

User Defined Function:
Defined by user at the time of writing the program.
There are three aspects of user-defined functions:
 Function Declaration, also known as function Prototype
 Function Definition
 Function call or function invocation
1) Function Declaration:
Introduces the function name, function return type, and function parameters to the program.
The declaration is terminated with a semicolon.
A function must be declared before it is used.
Syntax of Function Prototype:
return_type function_name (datatype1 name1, datatype2 name2, ..., typen namen);
parameter list
return type can be void, int, float or double.
function_name is any variable name.
datatype can be int, char, float or double. Parameter list can have 0 or more parameters. All
parameters need not be of same data type.
2) Function Definition:
also known as function implementation, means composing a function. Every Function definition
consists of two Parts: Header of the function and Body of the function.

The general form of header of a function is:
Note: The header of function is not terminated with a semicolon.
Body of the function:
{
st1;
st2;
….
return (value) //not required if return_type is void
}
The body of a function consist of a set of statements enclosed within braces.
The return statement is used to return the result of the computations done in the called function and/or
to return the program control back to the calling function.
3) Function Call:
Syntax:
function_name (parameter1, parameter2 , …);
variable_name = function_name (parameter1, parameter2 , …);
Function call always terminated with a semicolon.
Local Variables
int func1 (int y)
{
int a, b = 10;
float rate;
double cost = 12.55;
}
Those variables declared “within” the function are considered “local variables”. They can only be used
inside the function they were declared in, and not elsewhere.
return_type function_name (datatype1 name1, datatype2 name2, ...,typen namen)

To return a value from a C function, you must explicitly return it with a return statement.
Syntax:
return<expression>;
The expression can be any valid C expression that resolves to the type defined in the function header.
 Type conversion may occur if type does not match.
 Multiple return statements can be used within a single function (eg: inside an “if-else”
statement…)

Example C programs using User defined functions:
// function prototype (declaration)
int max(int a, int b);
int main()
{
int x;
x = max(5,8); // function call
x = max(x,7); // function call
}
int max(int a, int b) // function body
{
return a>b?a:b;
} // end of function
#include<stdio.h>
int twice(int x) // function body
{
x=x+x;
return x;
}
int main()
{
int x=10,y;
y=twice(x); // function call
printf("%d,%dn",x,y);
}

Abhineet

a) function with NO arguments and NO return value
b) function with arguments and NO return value

c) function with return value and NO arguments
d) function with arguments and return value

//Function with no input-output ( NO return value & NO arguments)
#include<stdio.h>
printsum(); //Function deceleration
void main() //main function, the master function
{ ………
printsum(); //Function Call
………. // from function, control returns to this statement in main
} // end of main
printsum() //definition of function printsum
{
printf("Sum of 2 and 3 is %d",2+3);
//Function with input and No output (with arguments but NO return value)
#include<stdio.h>
void printsum(int, int); //Function deceleration
main() //main function, the master function
{
int a,b;
printf("Enter values of a & bt");
scanf("%d %d", &a,&b);
printsum(a,b); //Function Call with actual arguments a, b
} // end of main
printsum(int x, int y) //definition of function printsum
{ // formal arguments x, y get the value of a,b
printf("Sum of %d and %d is %d",x,y,x+y);
Parameter Passing Methods in C:

1) Call (Pass)-by-Value Method:
Note: all the examples discussed above are examples of “call-by-value” method.
 In this method, the calling function passes the values of “actual arguments” to the called
function. However, these values are copied into “formal arguments” declared in the function
body. So, the changes made to these “local variables” inside the function, do not affect the
actual variables in the calling function.
 This is useful, when few parameters are to be passed.
Example: Swapping two integers using “Call-by-value” method

2) Call (pass)-by-Reference method:

Swapping two integers using “Call-by-Reference” method:

Passing array as parameter to Function:
#include <stdio.h>
double getAverage(int arr[ ], int size); /* function declaration */
int main ()
{
int balance[5] = {1000, 2, 3, 17, 50}; /* an int array with 5 elements */
double avg;
/* pass pointer to the array as an argument */
avg = getAverage( balance, 5 ) ; // function call with array as argument
/* output the returned value */
printf( "Average value is: %f ", avg ); // avg value is returned from function
return 0;
} // end of main
double getAverage(int arr[], int size) // function definition
{
int i; // local variable declarations
double avg;
double sum;
for (i = 0; i < size; ++i)
{ sum += arr[i];
}
avg = sum / size;
return avg;
/* Passing Array as Parameter to a function */
void mysort (int a[ ], int len); // function declaration
void main()
{
int i;
int tab[10] = {3,6,3,5,9,2,4,5,6,0};
for(i=0;i<10;i++)
printf("%d ",tab[i]);
printf("n");
mysort(tab,10); // function call with Array name as argument
for(i=0;i<10;i++)
printf("%d ",tab[i]); // display sorted array
printf ("n");
} // end of main
void mysort(int a[ ], int size) // function definition (body)
{
int i, j, x; // function to sort the array
for(i=0; i<size; i++)
{
for(j=i; j>0; j--)
{

if(a[ j ] < a[ j-1])
{ /* Change the order of a[ j ] and a[ j-1] */
x=a[ j ]; a[ j ]=a[ j-1]; a[j-1]=x;
} // end of if
} // end of inner for loop
} // end of outer for loop
Passing String as Argument to a function:

Recursive Functions:
Factorial Program: a) without function
Factorial Program: b) with function

Factorial Program: c) with Recursive function
// This function returns the sum of natural numbers 1 to num
int sum (int num)
{
int result;
if (num == 1)
result = 1;
else
result = num + sum (n-1);
return result;
}

2) Fibonacci Series program: a) without function
b) Fibonacci series using Recursion
important drawbacks of recursion
_ Function-Call Overhead
_ Memory-Management Issues

Standard Library Functions in ctype.h

Lk module3

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Lk module3