C programming session 08

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Programming in C
In this session, you will learn to:
Implement modular approach in C programs
Use library functions for string manipulation
Work with data storage types
Objectives

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Programming in C
Implementing Modular Approach in C Programs
Functions are the building blocks of C.
Every C program must consist of at least one function,
main().
The main() function is the entry point of a C program.

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Programming in C
Advantages of Functions
Functions:
Allow reusability of code and structuring of programs.
Provide programmers a convenient way of designing
programs.

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Programming in C
Parameters of Functions
A parameter:
Is the data that the function must receive when called from
another function.
May or may not be present in a function.
Of a user-defined function is declared outside the {} of that
function.

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Programming in C
Practice: 5.1
1. From the following program, identify the functions invoked
from main(), and state which functions have parameters.
Also state the parameters.
Microsoft Office
Word 97 - 2003 Document

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Programming in C
Practice: 5.1 (Contd.)
Solution:
1. The standard functions used in this program within main() are
as follows:
scanf() – parameters are format of input, and pointers to the
variable(s) in which the input must be stored
fflush() – parameter is stdin
The user-defined functions are:
output() – no parameters
calc() – one parameter, g, an int type data

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Programming in C
Invoking Functions
Functions that have parameters are invoked in one of the
following ways:
Call by value: In call by value, the called function cannot refer
to the variables of the caller function directly, but creates its
own copy of the values in different variables.
Call by reference: In call by reference, the called function
should be able to refer to the variables of the caller function
directly, and does not create its own copy of the values in
different variables. It is possible only if the addresses of the
variables are passed as parameters to a function.

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Programming in C
Passing Arrays to Functions
Arrays are inherently passed to functions through call by
reference method.
An array can be passed to a function in the following way:
Function name (array name);

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Programming in C
Practice: 5.2
1. If the variable avar is passed to a function by a call by
reference, can the value of the variable avar be modified in
the called function? Give reasons for your answer.
2. State whether True or False:
When an array is passed to a function, the array elements
are copied into the parameter of the function.
3. Consider the program code given in the following file.
Microsoft Office

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Programming in C
Based on the code, answer the following questions:
a. The function (max() / min()) is invoked by a call by value.
b. The function (max() / min()) is invoked by a call by reference.
c. After the function max() is executed, where does the control go to:
i. The min() function.
ii. The first line of the main() function.
iii. The first line of the main() following the line on which max() was invoked.
d. After execution of the function min(), program execution:
i. Stops without returning to main().
ii. Goes back to the main() function.
e. If the values of i and j were to be printed after the function max() and
again after the function min(), what values would be displayed?

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Programming in C
4. Write a program that calls a function called power(m,n),
which displays the nth power of the integer m (m and n are
parameters). The function must be invoked by a call by
reference.

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Programming in C
Solution:
1. Yes, because the addresses of the variables are passed in by
using call by reference, the memory locations of the variables
are known to the function. Using pointers to the variables, their
values can be modified.
2. False. Values of variables are copied into the parameters only
in the case of a call by value.
3. a. max()
b. min()
c. iii
d. ii
e. After max() is executed, the values of i and j printed out
would be the same as those entered during execution. After
min() is executed, the value of i would still be the same, but
j would increase by 5 (since b is a pointer to the variable j).

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Programming in C
4.main() {
int x, y;
printf(“Enter Number: ”);
scanf(“%d”, &x);
fflush(stdin);
printf(“Enter power raise to : “);
scanf(“%d”, &y);
fflush(stdin);
power(&x, &y); }
power(m,n)
int *m, *n; /* power is pointed to by n,
value is pointed to by m */
{ int i=1,val=1;
while(i++<= *n)
val = val ** m;
printf(“%d the power of %d is %dn”, *n,*m,
val);}

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Programming in C
Returning Values from a Function
A function can return a value to the caller function.
The return statement is used to send back a value to the
caller function.
The return statement also transfers control back to calling
function.
The default return value is int type.
The return statement can return only one value.
The syntax for the return statement is:
return[expression]
A function can also return an array. This could be done by:
return [array name]

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Programming in C
Practice: 5.3
1. Point out the error(s), if any, in the functions given in the
following file:
2. The following program should calculate the square of any
float value, using a function called square(). The float value
is an input to the program. The program is incomplete. Put
in the appropriate statements in the program given in the
following file:
Microsoft Word
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Microsoft Word
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Programming in C
3. The function, makeint(), was coded to convert any
number entered into a char array to integer type. The
function takes the string as parameter and returns the
value, as given in the following file:
Microsoft Word
Document

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Programming in C
Solution:
Microsoft Word
Document

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Programming in C
Command-Line Arguments
Command-line arguments:
Are the parameters that the main() function can receive from
the command line.
Are passed as information from the OS prompt to a program.
The main() function has 2 arguments, argc and argv.
The format of the main() function with parameters is as
follows:
main(argc, argv)
int argc;
char *argv[];
{
:
}
Here, argc is integer and argv is a character array of
unlimited size (hence [ ] in the declaration).

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Programming in C
Practice: 5.4
1. Given that a C program called temp is executed by the
following command:
temp start 6
match the following:
a. value of argc 1. points to array "6"
b. argv [0] 2. points to arrm/ "start"
c. argv [1] 3. 3
d. argv[2] 4. points to array "temp"
2. Modify the program upper so that it first checks the number
of arguments entered on the command line. The program
should display an error message if no arguments have been
entered and also allow conversion of as many strings to
upper-case as have been specified as arguments on the
command line.

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Programming in C
3. Consider the following program to calculate the sum of 2
integers specified on the command line:
main (argc, argv)
int argc;
char *argv [ ];{
sum (argv [1], argv [2]);
}
sum (num1, num2)
int numl, num2;{
return numl + num2;
}
The program has some logical errors. Point out the errors and
correct the code.

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Programming in C
Solution:
Microsoft Word
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Using Library Functions for String Manipulation
Library functions:
Are also known as built-in functions.
Can be used by including the concerned header files.

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Standard String-Handling Functions
Some of the standard string-handling functions are:
strcmp(): Compares 2 strings (its parameters) character by
character (ASCII comparison).
strcpy(): Copies the second string to the first string named
in the strcpy() parameters.
strcat(): Appends the second string passed at the end of
the first string passed to it .
strlen(): Returns the number of characters in the string
passed to it.

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Programming in C
Practice: 5.5
1. What will the following function call return?
x = strcmp(“Cada”, “CADA”);
What should the declaration of x be?
2. Assume that array contains the string 846*.
What will array contain when the following statement is executed?
strcat(array,”>”);
3. State whether True or False:
The following statement returns a value of 4 to x.
x = strlen ("abc");

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Programming in C
Solution:
1. Value returned - 32
Declaration - int x;
2. 846*>
3. False

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Programming in C
String to Numeric Conversion Functions
Conversion functions:
Are available as a part of the standard library.
Are used to convert one data type into another.
The following functions are used to convert a string to a
numeric value:
atoi(): Returns the int type value of a string passed to it
and the value 0 in the case the string does not begin with a
digit.
atof(): Returns the double type value of a string passed to it
and the value 0 in the case the string does not begin with a
digit or a decimal point.

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Programming in C
Practice: 5.6
1. What value will the variable val contain in each of the
following situations?
a. val = atoi ("A345"); /* val is int type */
b. val = atof ("345A"); /* val is double type */

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Programming in C
Solution:
1. a. 0
b. 345.000000

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Programming in C
Functions for Formatting Data in Memory
The formatting functions are available as a part of the
standard library.
The following functions are used to format data in memory:
sprintf():
Writes to a variable in the memory and stores the data in different
variables specified.
Are used for transferring data between variables in a specific
format.
Has the following syntax:
sprintf(string, format-specification, data, ….);
sscanf():
Performs formatted input from a string.
Has the following syntax:
sscanf(string, format-specification, data, ….);

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Programming in C
Practice: 5.7
1. What data is assigned to the variable string by each of the
following?
a. sprintf(string,"%04d%3.2f%2s",21,4.576, "Hi“);
b. sprintf (string, "%10s", "ABC");
c. sscanf ("0987APZ", "%4d%s", &num, string);
1. What is the error, if any, in the instructions given below
against each purpose? Give the correct instruction in case
of an error.
Purpose Instruction
Accept a name from keyboard printf(“%s”, name);
Format the contents of variables
i_num(int) and f_num(float), and store
them into a character array called string.
printf (string,"%d%f, i_num,f_num)

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Programming in C
Solution:
Microsoft Word
Document

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Programming in C
Working with Data Storage Types
C language provides the following data storage types:
auto: Variables of this type retain their value only as long as
the function is in the stage of execution.
static: Variables of this type retain its value even after the
function to which it belongs has been executed.
extern: Variables of this type are declared at the start of the
program and can be accessed from any function.

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Programming in C
Practice: 5.8
1. Given the following declarations:
float area;
static float val;
auto char number;
State which variable(s) will be:
a. Created each tune the function is invoked.
b. Created only once.
2. A numeric array has to store 4 values - 2.5, 6,3, 7.0 and 8.0.
This array is to be declared and used in a function called
compute(). Which of the following is/are correct
declarations of this array?
a. static int values[4] = {2.5,6.3,7.0,8.0};
b. auto float values[4] = {2.5,6.3,7.0,8.0 };
c. float values [4]= {2.5,6.3,7.0,8.0};
d. static float values [4] = {2.5,6.3,7.0,8.0};

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Programming in C
Solution:
1. a. area, number
b. val
2. (a) Is invalid because the array should be float or double type.
(b) Is invalid because it is declared as auto type.
(c) Is invalid because it is declared as auto type.
(d) Is correct.
.

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Programming in C
Practice: 5.9
1. If the variable val is declared as global in the program B,
just illustrated, how would program A be modified? Give the
appropriate declarations required in both programs.
2. Consider the following 2 program files:
Program A
float x;
calc() {
int i;
: } printout()
{ static char z;
: }
Program B
char numarray[5];
main() {
char c ;
: }

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Programming in C
Based on this code, answer the following:
a. The variable z can be accessed in the function(s)
____________________.
b. The variable(s) that can be accessed from functions of both program
files is/are ___________.
c. Slate whether True or False:
The variable i can be used in the function printout().
d. Memory for variable z is reserved each time the function printout()
is invoked. State whether true or false.
e. If the function printout() has to access the variable x, does x have
to be declared within the function printout()?
If so, give the declaration.
f. The auto variable(s) in these programs is/are _________________.

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Programming in C
Solution:
1. In program B, val would be declared as follows:
int val;
calc(){
:}
In program A, the declaration would be as follows:
main()
{ extern int val;
:}
2. a. printout() only (Since it is declared within the function
printout() and hence is not global)
x and numarray (if proper extern statements are coded).
b. False (Since it is declared within the function calc(), and
hence it is not global)

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Programming in C
c. False (Since z is a static variable, it is created only
once – the function printout() is invoked.)
d. No (Since x is declared as global in program A, and
printout() is defined in the same program file. However,
declaring it as extern while within printout() is wrong.)
e. The variable i defined in calc() and the variable c defined
in main().

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Programming in C
Practice: 5.10
1. The following file contains a C program called remdigit.c
and a list of errors in the program indicated by the compiler.
Go through the error list and correct the program. Since the
C compiler does not always give very meaningful error
messages, go through the program given in the following
file carefully.
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Programming in C
2. Write a program to display all the positions at which a
character occurs in a string. Both the character to be
located and the string to be searched should be passed to a
function called nextpos (findchar, searchstr).
Each time the function locates the diameter, it should pass
back the position.
After searching the entire string, the function should return
the value -1.

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Programming in C
Solution:
Work out your answers. A discussion on these follows in the
Classroom.

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Programming in C
Summary
In this session, you learned that:
Functions provide advantages of reusability and structuring of
programs.
A parameter of a function is the data that the function must
receive when called or invoked from another function.
Functions that have parameters are invoked in one of the
following two ways:
Call by value
Call by reference
Call by value means that the called function creates its own
copy of the values in different variables.
Call by reference means that the called function should be able
to refer to the variables of the caller function directly, and does
not create its own copy of the values in different variables.

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Programming in C
Summary (Contd.)
Arrays are passed to functions by the call by reference
method.
Functions can return values by using the return statement.
The main() function can have parameters, argc and argv.
argc is integer type while argv is a string.
The information that is passed to a program from the OS
prompt is known as command-line arguments.
Some of the standard string-handling functions are:
strcmp(): Compares two strings.
strcpy(): Copies the second string to the first string.
strcat(): Appends the second string passed at the end of the
first string passed as parameters.
strlen(): Returns the number of characters in the string
passed as a parameter.

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Programming in C
Summary (Contd.)
atoi(): Returns the int type value of a string passed to it.
aof(): Returns the double type value of a string passed to it.
The following functions are used to format data in memory:
sprintf()
sscanf()
C language provides the following data storage types:
auto: Variables of this type retain their value only as long as the
function is in the stage of execution.
static: Variables of this type retain its value even after the
function to which it belongs has been executed.
extern: Variables of this type are declared at the start of the
program and can be accessed from any function.

C programming session 08

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