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NIIT SEM Q/CPR/CR/SESSION 5/1/VER06/95

REVIEW QUIZ

#1 Through the following function, swap (a, b),the values of 2 variables passed to it have to

be swapped :

swap (a, b)

int a, b;

{

int temp;

temp = a;

a = b;

b = temp;

return (a);

return (b);}

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REVIEW QUIZ (Contd.)

The function is invoked from main () and thevalues of variables x an y are passed to it.

a. Is the function syntactically correct?

b. Is the function logically correct?

c. Will the function interchange the values of

the variables x and y?

If not, give the correct code.

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#2 Study the following C statements of 2 programfiles :

/* Program A * / /* Program B */

main () int x = 0;

{ count (charac, str)char c, locate [20]; {

count (&c, locate); int I = 0;

printf (%d, x); while(str [i] != \0)

} if (str [i+ + ] = = charac)

x+ + ;

}

What declarations have to be included /modified in each of these programs ?


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#3 A program called find expects one valuefrom the command line which is a string.How are these parameters accepted by theprogram?

Give all parameter declarations and their

values when the following command isentered at the $ prompt:

Find The


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#4 Given the following return statement of afunction called ret_val ():

return (float) rate * unit_sold;

which of the following declaration (s) for thefunction ret_val() should be included in themain program?

a. void ret_val ();b. int ret_val ();

c. float ret_val ();

d. No declaration is necessary


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#5 Given that a char array has to be assignedthe string:

LOOKUPPAGE

state whether true or false.

The array may be declared to be either autoor extern or declared globally, but not static.


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#6 What are the values of a and b after the fourth

time the following function is invoked?

find_type (c)

char c;

{ static int a = 0, b; b = 0;

if ((c > = A) && (c < = Z))

a+ + ;

else if (( c > = a) && (c < = z))b+ + ;

}

Assume that the values of c passed in the 4

function calls are :

A b c D


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#1 a. Yes

b. No, because a function cannot return 2values.

c. No, since it is a call by value, the values of

x and y get copied to memory variables aand b respectively. The changes to theseare not reflected in x and y.

A call by reference should be made insteadof a call by value.

So, the correct code is :

SOLUTIONS TO REVIEW QUIZ

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swap (a, b) /* interchange *a and *b */

int *a, *b;

{

int temp;

temp = *b;*b = *a;

*a = temp;

}

#2 In program A:

extern int x; /* within main () */

In program B:

char *charac, str []; /* after count (charac,str) */


(Contd.)

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#3 The declarations are :main (argc, argv)

int argc;

char *argv [];

Value of argc will be 2.Value of argv [0] will be find.

Value of argv [1] will be The.

#4 c.

#5 False

#6 The variable a will be 2.

The variable b will be O (b gets initialized

each time the function is invoked).


(Contd.)

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Objectives

At the end of this session, you will be able to:

Write C programs that invoke functionsthrough :

Call by reference Call by value

Write C programs using void type functionsand functions that return values of different

data types Explain the structure of the function main ()

and write C programs which handle commandline parameters

SPL SESSION

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Objectives (Contd.)

State the features of the following datastorage types :

Auto

Static

Extern

and use these in single and multiple Cprogram files

Use the following standard string comparisonfunctions of c:

strcmp ()

strcpy ()

strcat ()

strlen ()

SPL SESSION (Contd.)

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Objectives (contd.) Use the following string to numeric conversion

function:

atoi ()

atof () Use the following functions for formatting

strings in memory:

sscanf ()

sprintf ()

SPL SESSION (Contd.)

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Data that the function must receive when calledfrom another function

A function may/may not have parameters

Example

main (){

disp_head ();

}

disp_head () /* no parameters */{

printf (EMPLOYEE REPORT);

}

disp_head () does not have parameters

PARAMETERS OF A FUNCTION

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Example

The following function has two parameters, aand b:

main ()

{:

sum (x, y);

}

sum (a, b) /*2 parameters */int a, b;

{

int value;

value = a + b;

}


(Contd.)

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Parameters are of same data type as that ofvalues received

Declarations must be made outside opening bracefor function

Parameters may be passed :

By value

By reference


(Contd.)

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Values of variables passed get copied into the

memory locations of the parameters

Example

Contents of main ()

{

num1 num2 operator :

2 3 * calc (num1,

num2,operator

:2 3 * }

val1 val2 oper calc (val1, val2, oper)

int val1, val2;

char oper;

{ : }

INVOKING FUNCTIONS

THROUGH CALL BY VALUE

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Addresses of variables passed get copied intothe memory locations of the parameters

Example

Contents ofnum1 num2 operator main ()

105 120 13 {

2 3 + :

addresses passed calc ( &num1,

105 120 130 &num2 ,&oper);

val1 val2 oper :

}

INVOKING FUNCTIONS

THROUGH CALL BY

REFERENCE

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2 + 3 calc (val1, val2, oper)

int *val1, *val2;

val1 points to num1 char *oper;

val2 points to num2 {

:

:printf (%d,*val1+ *val1);

}

INVOKING FUNCTIONS

THROUGH CALL BY

REFERENCE (Contd.)

INVOKING FUNCTIONS

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Arrays are inherently passed through call byreference

Example

main ()

{

int str [10];

:

stringfunc (str);}

stringfunc (number_list)

int number_list [ ]; /* no subscript*/

{: }

INVOKING FUNCTIONS

THROUGH CALL BY

REFERENCE (Contd.)

INVOKING FUNCTIONS

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ORstringfunc (number_list)

int number_list [ 10 ]; /* same size asnum_array*/

{

:

}

ORstringfunc (number_list)

int *number_list: /* int type pointer because */

/* number_list is int type array */

{ :}

INVOKING FUNCTIONS

THROUGH CALL BY

REFERENCE (Contd.)

RETURNING VALUES FROM

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The return Statement

Sends back one value to the caller

Example

sum (a, b)

int a, b;{

return a + b; /* value of a + b returned */

}

Different values may be returned based onconditions


FUNCTIONS


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Example

diff (a, b)

int a, b;

{

if (a > b)return a - b;

else if (b > a)

return b - a;

else

return O;

}

Default return value is int type

Also transfers control back to calling function


FUNCTIONS


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Other data types may also be returned

Example

main ()

{

float sum (); /* function declared float */float x, y, value ;

scanf (%f, &x, &y);

fflush (stdin);

value = sum (x, y);

printf (Total is %f\n, value);

}


FUNCTIONS (Contd.)


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float sum (a, b) /*function declared float */float a, b;

{

return a+b;

}

Function must be declared as type of value itreturns


FUNCTIONS (Contd.)

Void TYPE FUNCTIONS

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Functions that simply return control to caller

without returning a value

Example

main ()

{void sum (); /* sum () declared void */

float x, y; scanf (%f %f, &x, &y); sum (x, y);

}

void sum (a, b)float a, b;

{

printf (%f, a + b);

return; /* sends control back */

}

Void TYPE FUNCTIONS

THE i () FUNCTION

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Standard type of parameters are used toreceive arguments from command line

main (argc, argv)

int argc;

char *argv [ ];{

:

}

argv 100 106 125 135

argv [0] 100

argv [1] 106

: : :Pointer to an Array

THE main () FUNCTION


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Usage of Command Line Arguments

Upper Abracadabra (entered on command line to

execute a program called upper)

argc =2 (2 words entered at command line)

argv [0] 100 u p p e r /0

(first word on command line)

argv [1] 106 A b r a c a d a b r a /0

(second word on command

line, i.e. first argument)

Pointer to an Array (char type)


(Contd.)

DATA STORAGE TYPES

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Storage Created Initialized Can be

Type accessed

auto Each time Can be initia- Only in the

(default) the function lized at time function inis invoked of declara- which

tion or later declared

static The first time Initialized at Only in the

the function time of decl- function in

is invoked aration so whichthat the value declared

is not reset;

static arrays

can also be initialized

DATA STORAGE TYPES

DATA STORAGE TYPES (Contd )

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Storage Created Initialized Can be

Type accessed

extern Created at Initialized In any

the time where decl- function

where declared global in sameared as global since mem- /different

but not where ory is reser- program

declared ext- ved then file

ern

DATA STORAGE TYPES (Contd.)

STANDARD STRING-HANDLING

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STRCMP ()

Compares 2 strings (its parameters) characterby character (ASCII comparison)

Returns any of the following integer values :

Return value Meaning Example

< 0 ASCII value of y= strcmp (ABC,

character of first abc);

string is less than returns-32 (ASCII

that of correspon- differenceding character of between A and a)

second string

STANDARD STRING HANDLING

FUNCTIONS


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Return value Meaning Example

0 Strings are identi- y = strcmp (ABC,

cal ABC);

returns 0

> 0 ASCII value of y = strcmp (abc,character of first ABC);

string is greater returns 32 (ASCII

than that of corre- difference

sponding charac- between a and Ater of second stri-

ng

FUNCTIONS (Contd.)


FUNCTIONS

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strcpy ()

Copies second string to the first string namesas the parameter

Example

strcpy (str1, ABC);

copies string ABC to array str1

strcpy (str1, str2);

copies contents of array str2 to array str1

Current contents of first array are lost

FUNCTIONS


FUNCTIONS (C td )

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strcat ()

appends second string passed to it to end offirst string passed to it

Example

strcat (str1, ABC);

adds string ABC to current contents of str1

strcat (str1, str2);

adds contents of array str2 to current contents

of str1

FUNCTIONS (Contd.)


FUNCTIONS (C td )

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strlen ()

Returns length of string passed to it

Length does not include NULL character

Example

If str1 contains 1234y = strlen (str1);

then y = 4

FUNCTIONS (Contd.)

STANDARD STRING - TO -

NUMERIC

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atoi ()

Returns int type value of string passed to it;returns 0 if string does not begin with digit

Example

If str1 contains string 1234

y = atoi (str1);

then y = 1234

If str1 contains string ABCy = atoi (str1);

then y = 0

NUMERIC

CONVERSION FUNCTIONS

STANDARD STRING - TO -

NUMERIC

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atof ()

Returns double type value of string passed to it;returns O if string does not begin with digit for decimal

pointExample

If str1 contains string 1234

y = atof (str1);

then y = 1234.000000Following declaration must be included in program:

double atof ();

since it returns a non-integer value

NUMERIC

CONVERSION FUNCTIONS

(Contd.)

FORMATTING DATA IN

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sprintf () formats data and can control the

width of the destination string

Syntax

sprintf (string, format-specification, data, );

where:

string is a pointer to destination string in

memory which will contain

formatted data as per format-

specificationformat- is specification of how data is to be

specification formatted

data, is list of data to be formatted

MEMORY

FORMATTING DATA IN

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Example

sprintf (str, %02s-%02s-%02s, 28, 8, 89);printf (str contains : %s\n, str);

Output

str contains : 28-08-89

MEMORY (Contd.)

FORMATTING DATA IN

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sscanf() assigns different parts of a string to

different variablesSyntax

sscanf (string, format-specification, variable, );

where :

string is a pointer to source string in

memory which contains data to

be assigned to the list of variables

according to format-specificationformat- is the specification of how data is

specification to be formatted

variable, is the list of variables to which the

data would be assigned after

formatting

MEMORY (Contd.)

FORMATTING DATA IN

MEMORY (C td )

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Example

sscanf (str, %2d%2s%s%d, &day, suffix,

mnth, & year);

printf (The day is: %d, suffix is: %s, month is:

%s, year is: %d\n, day, suffix, mnth, year);

Example

If the data in str is 28th August 1989:

The day is : 28, suffix is:th, month is : August,year is: 1989

MEMORY (Contd.)

SPL EXERCISE

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#1 Given below is a C program called remdigit.c

and a listing of errors in the program indicatedby the compiler. Go through the error listingand correct the program. Since the C compilerdoes not always give very meaningful error

messages, go through the program carefully.1 /* search for the number of digits in aninput string and

2 copy all characters except digits into

another string*/3

4 main ()

5 {

6 char inp , out [];

SPL EXERCISE (Contd.)

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7 int numb = I = j = 0;

8

9 printf (Enter string :);

10 gets (inp);

11 fflush (stdin);12

13 while (inp [i] != \0)

14 {

15 if (inp [i] > = 0 && inp [i] < = 9)16 number+ + ;

17 else

18 out [j+ + ] = inp [i];

19


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20 }

21

22 printf (Number of digits in string were :%c numb);

23 printf (String without digits is %s, out);

24

25

Error listing :

remdigit.c, line 7: i undefined

remdigit.c, line 7: j undefined

remdigit.c, line 9: Enter undefined


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Error listing (Contd.):

remdigit.c, line 9: syntax error

remdigit.c, line 11: stdin undefined

remdigit.c, line 13: illegal indirection



remdigit.c, line 16: number undefined

remdigit.c, line 18: illegal indirectionremdigit.c, line 22: syntax error

remdigit.c, line 25: syntax error

SOLUTION TO SPL EXERCISE

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#1 /* search for the number of digits in an input

string and copycopy all characters except except digits into

another string */

# include < stdio.h>

main ()char inp [80] , out [80];

int I, j, number;

number = i = j = O;

printf (Enter string :);

gets (inp);

fflush (stdin);


(Contd )

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while (inp [i] != \O)

{if (inp [i] > = O && inp [i] < = 9

number+ + ;

else

out [j+ + ] = inp [i];

i+ + ;

}

printf (Number of digits in string were : %d,number);

printf (String without digits is %s, out);

}

(Contd.)

SPL EXERCISE

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#2 Write a program to display all the positions atwhich a character occurs in a string. Both thecharacter to be located and the string to besearched should be passed to a functioncalled nextpos (findchar, searchstr). Each time

the function locates the character, it shouldpass back the position.

After searching the entire string, the functionshould return the value -1.


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#2 #include < stdio.h>

main ()

{

int occur = O;

char str [100], whichchar;

printf (Enter a string of upto 99 characters \n);

scanf (%99s, str);

fflush (stdin);

printf (Enter character to be located : );scanf (%c, &whichchar);

fflush (stdin);


(Contd )

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while ((occur = nextpos (whichchar, str +

occur )) != -1{

printf (The character %c occurs in the

string at position %d \n, whichchar, occur);

}

}

nextpos (findchar, searchstr)

char findchar, *searchstr;{

static int i=0;

(Contd.)


(Contd.)

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while (searchstr [i] != \0

{

if (searchstr [i+ + ] = = findchar)

return i;}

return -1;}

(Contd.)

CLASSROOM EXERCISE

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#1 Alcatel Automatics is a company known for its

marketing success. This success has beenlargely due to its superb data analysisprograms.

The Product Manager wants some

modifications to the existing programs.When running the program, he should be ableto specify any of the following with the runcommand itself :

%s for displaying the product sales by eachsalesman as a percentage of the totalsalesman sales

%p for displaying the product sales by each

salesman as a percentage of the total productsales

CLASSROOM EXERCISE

(Contd.)

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%i for displaying the product sales as an index

of total sales of all products

He should also be shown some help messageto assist him in case he forgets what to specifywith the command and should then be able togive the command again.

Since the calculations done in this program areto be used in some other data analysisprograms also, it has been decided that thecalculations will be coded in separate functionswhich are stored together in one file called

func. C, separate from the main () function.

(Contd.)

CLASSROOM EXERCISE

(Contd.)

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The functions available in this file are :

inddat () this displays the data as an index oftotal sales

proddat () this displays the data as apercentage of total product sales

calcprodtot () this calculates the product-wise totals

calcsaltot () this calculates thesalesman-wise totals

(The code of the file func.c is provided in yourLearner Guide).

Write the code for the function main (). In casethe %s option is chosen, print the message

Module not ready yet.

( )

CLASSROOM EXERCISE

(Contd.)

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as the function to display product sales as a

percentage of the total salesman sales has notbeen coded in func.c as yet.

Hints for Classroom Exercise

a. Check first argument. If invalid, display

message.b. Input data into 2-d array. Array is declared

global so that is available to all other functions.

c. Declare array as extern in other functions.

d. Depending on first argument, call appropriatefunction.

e. exit () function terminates program execution.

( )

SOLUTION TO CLASSROOM

EXERCISE

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#1 # include < stdio.h>

main (argc, argv)int argc;

char *argv [ ];

{

extern float salesdat [4] [4], prodtot [4],salestot [4];

extern int ind, row, col;

/* check parameter count and first argument*/


EXERCISE (Contd.)

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if ((argc != 2) && (strcmp (argv [1], %I) !=

0) && (strcmp (argv [1], %p) != 0) &&(strcmp (argv [1], %s) != 0))

{

printf ( Usage : sales [%s] [%p] [%i]\n);

exit ();

}

if (argv [1] [1] = = s)

}printf (\nModule not ready yet.);

exit ();}

( )


EXERCISE (Contd.)

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/* input sales data into 2-d array */

for (row = O; row < 4; row+ +)

{

printf (Enter sales figures for salesman %d

:\n, row + 1);

for (col = O; col < 4; row+ +)

{

scanf (%f, &salesdat [row] [col]);

fflush (stdin);

}

}

( )


EXERCISE (Contd.)

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/* execute appropriate function depending on

first argument */

if (strcmp (argv [1], %p) = = O)

proddat ();

else if (strcmp (argv [1], %i) = = O)

inddat ();

}

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