C Programming : Arrays and Functions

C Programming : Arrays and Functions
By
Mr.S.Selvaraj
Asst. Professor (SRG) / CSE
Kongu Engineering College
Perundurai, Erode, Tamilnadu, India

20CST11 – Problem Solving and Programming
2/11/2021 3.1 Arrays 2
Syllabus

Contents
1. Arrays
– Declaring and initializing 1D array
– Two dimensional arrays
– Multidimensional arrays
2. Functions
– Basics, The anatomy of a function
– Types of functions based on arguments and return types
– Passing 1D and 2D arrays as arguments to functions
– Calling function from another function
3. Recursive functions
4. Variable scope and lifetime
5. Storage classes.
2/11/2021 3
3.1 Arrays

Introduction
• Variables can’t handle voluminous data because a
hundred data items need a hundred variables to store
them.
• The solution is to use an array, which is an ordered set
of data items stored contiguously in memory.
• Each data item represents an element of the array and
is accessed with an index or subscript.
• For instance, the elements of an array named signal
are accessed as signal[0], signal[1], signal[2], and so
forth.
• The first subscript is 0 and the last subscript is one less
than the size of the array.
2/11/2021 3.1 Arrays 4

Introduction
• The elements of an array have a common
data type (like int, char, etc.).
• An array must be declared with its type and
size to enable the compiler to allocate a
contiguous chunk of memory for all array
elements.
2/11/2021 3.1 Arrays 5

Introduction
• The first element is accessed as signal[0] and the last
element is signal[31] (not 32).
• The subscript is either zero, a positive integer or an
expression that evaluates to an integer value.
• An array element can be assigned to a variable
– (say, int x = signal[2];),
– which means we can use signal[2] wherever we use x.
• By the same logic, &signal[2] is also a valid scanf
argument like &x.
• It is easy to cycle through all array elements by using
the array subscript as a key variable in a loop.
2/11/2021 3.1 Arrays 6

Introduction
• C doesn’t offer bounds checking for arrays, i.e. it doesn’t
validate the index used to access an array element.
• For instance, the compiler will not generate an error if you
attempt to access signal[35] even though the array has 32
elements.
• A negative index (as in signal[-5]) doesn’t generate an
error either.
• C also supports multi-dimensional arrays where an
element is handled with multiple subscripts.
• Since there is virtually no limit to the number of indexes
and dimensions an array can have.
• arrays in C are very powerful data structures that can
easily gobble up a lot of memory.
2/11/2021 3.1 Arrays 7

DECLARING AND INITIALIZING AN ARRAY
• The declaration of an array specifies its name, type and
size, which is normally specified as a constant or
symbolic constant.
• The following statement declares a single-dimensional
array named signal having 32 elements, each of type
int.
• The sizeof operator, when used on an array, returns the
total usage of all elements, so the below definition
allocates 32 × sizeof(int) bytes of memory—typically,
128 bytes.
2/11/2021 3.1 Arrays 8

Layout in Memory of the Array
• months[12] and MONTHS[12] are two
separate arrays.
2/11/2021 3.1 Arrays 9

Initializing During Declaration
• In the first declaration, the number of values matches
the size of the array.
• The second declaration performs a partial initialization
by assigning values to the first three elements only.
When that happens, the remaining values are
automatically initialized to zeroes (NUL for an array of
type char).
• The third declaration uses an empty pair of brackets
([ ]) to implicitly specify the size of the array.
2/11/2021 3.1 Arrays 10

INITIALIZING AND PRINTING ARRAYS
2/11/2021 3.1 Arrays 11

Inserting an Element in an Array
2/11/2021 3.1 Arrays 13

Deleting an Element from an Array
2/11/2021 3.1 Arrays 14

Reversing with Two Arrays
2/11/2021 3.1 Arrays 15

Reversing with a Single Array
2/11/2021 3.1 Arrays 16

SORTING AN ARRAY (SELECTION)
2/11/2021 3.1 Arrays 17

PROGRAM TO SEQUENTIALLY SEARCH AN ARRAY
2/11/2021 3.1 Arrays 19

TWO-DIMENSIONAL (2D) ARRAYS
• A two-dimensional array needs two subscripts
and a three-dimensional array needs three
subscripts.
• Like a single-dimensional array, a multi-
dimensional array occupies a contiguous region
of memory.
• A two-dimensional (2D) array, arr, takes the form
arr[i][j],
– where the subscript i represents the number of rows
and
– j represents the number of columns.
2/11/2021 3.1 Arrays 24

• Internally though, a 2D array can be viewed as
an array of single-dimensional arrays.
• This means that table represents a set of
three single-dimensional arrays of four
elements each.
• Alternatively, it can be considered as three
rows having four columns in each row.
2/11/2021 3.1 Arrays 25

Full Initialization During Declaration
2/11/2021 3.1 Arrays 27

Partial Initialization During Declaration
2/11/2021 3.1 Arrays 28

MULTI-DIMENSIONAL ARRAYS
• Multi-dimensional arrays in C can go beyond two
dimensions.
• Every increase in dimension increases he number of
subscripts by one, with the subscript on the right changing
faster than the one on the left.
• A three-dimensional (3D) array can be treated as an array
of arrays of arrays.
• In this case, only those elements accessed with the right-
most subscript—with the other subscripts remaining
unchanged—occupy consecutive memory cells.
• visualization of an array becomes difficult when the
number of dimensions exceeds three.
2/11/2021 3.1 Arrays 30

USING ARRAYS AS MATRICES
2/11/2021 3.1 Arrays 32

Transposing a Matrix
2/11/2021 3.1 Arrays 33

Adding and Subtracting Two Matrices
2/11/2021 3.1 Arrays 34

Multiplying Two Matrices
2/11/2021 3.1 Arrays 36

Thank you
2/11/2021 3.1 Arrays 38

C Programming : Functions
By
Mr.S.Selvaraj

Contents
1. Arrays
2. Functions
5. Storage classes.
2/11/2021 40
3.2 Functions

Introduction
• C programmers decompose a complex task into
independent and manageable modules called
functions.
• A function is a statement that represents a named
body of program code.
• When it is called or invoked, the code associated with
the function is executed.
• A function can optionally
– (i) accept one or more values as arguments, and
– (ii) report the outcome of its action by returning a single
value to the caller.
• A function is called mainly in one of these two ways:
2/11/2021 3.2 Functions 41

Introduction
• A function is easily identified from the matched
pair of parentheses that follow its name.
• A function must be declared and defined before
it is called or invoked.
• The declaration specifies how to invoke the
function correctly.
• The definition provides the implementation, i.e. ,
the body of code that will be executed on
invocation
2/11/2021 3.2 Functions 42

Introduction
• The functions you create can also call other
functions.
• A function can even call itself, a property that
has important applications in the programming
world (like calculating the factorial of a number).
• For all of the functions we have used so far, we
had main as the caller.
• This is a special function that every standalone C
program must have because a program
commences execution by calling main.
2/11/2021 3.2 Functions 43

NO ARGUMENTS, NO RETURN VALUE
2/11/2021 3.2 Functions 44

• The return; statement in the function has the same
significance as the one we have all along used in main.
• It terminates the function and returns control to the caller.
• However, this function doesn’t return a value (return; and
not return 0;).
• Even though a return here is not necessary, it’s good
programming practice to include it in every function even
though it may return nothing.
2/11/2021 3.2 Functions 46

THE ANATOMY OF A FUNCTION
• Main attributes of functions:
– Declaration
– definition and
– invocation
2/11/2021 3.2 Functions 47

Declaration, Prototype or Signature of Function
• A declaration is an authentic statement that tells the
compiler how the function is invoked.
• The declaration is also known as prototype or signature.
• Since it is placed before main, the compiler sees it first and
then compares it to the invocation and definition.
• For this comparison, the compiler determines whether the
function
– uses any arguments, and if so, the number of such arguments
along with their data types.
– returns a value, and if so, its data type.
• This creates four possible situations—
– with or without arguments, and
– with or without return value.
2/11/2021 3.2 Functions 48

Declaration, Prototype or Signature of Function
• The first void indicates that the function doesn’t
return a value.
• The second void signifies that the function uses no
arguments.
• An argument can be a variable, constant or expression
2/11/2021 3.2 Functions 49

• The area function accepts two arguments each of type
float and returns a value of type double.
• Since the compiler simply matches the type and
number of arguments in the declaration with those
used in the definition.
• It doesn’t need to know these variable names, and C
lets you omit them.
2/11/2021 3.2 Functions 50

Definition or Implementation
• The function definition or implementation specifies what the
function does when invoked.
• It comprises a header and a body where all the work gets done.
• For a function that accepts arguments and returns a value.
2/11/2021 3.2 Functions 51
• The header (the first line) is virtually identical to the declaration
except that there’s no semicolon as terminator.
• The body is represented by a simple or compound statement that is
compulsorily enclosed within curly braces.
• The return statement transmits the value of expression back to the
caller.

Invocation or Call
• The programmer must invoke the function in
a way that enables the program to “see” the
value.
• Typically, the return value is saved in a
variable or used as an argument to another
function.
2/11/2021 3.2 Functions 53

Types of functions based on arguments and
return types
1. Function Without Return Values and Without Arguments.
2. Function Without Return Values and With Arguments.
3. Function With Return Values and Without Arguments.
4. Function With Return Values and With Arguments.
2/11/2021 3.2 Functions 54

Function Without Return Values and Without Arguments.
2/11/2021 3.2 Functions 55

Function Without Return Values and With Arguments.
2/11/2021 3.2 Functions 56

Function With Return Values and Without Arguments.
2/11/2021 3.2 Functions 57

Function With Return Values and With Arguments.
2/11/2021 3.2 Functions 58

Parameter Passing: Arguments and Parameters
• To understand the concept of parameter passing, we need to look
at function arguments from two viewpoints—the caller and called
function.
• When the caller (here, main) invokes a function, it assigns values to
the arguments or actual arguments of the function.
• The called function accepts these values into its parameters or
formal arguments.
• When we invoke c2f as shown above, the value of celsius (the
argument) is assigned to f_celsius (the parameter).
• This transfer of value from argument to parameter is known as
parameter passing.
• argument means the “actual argument” and parameter means the
“formal argument” to a function.
2/11/2021 3.2 Functions 59

Passing by Value
• The question is whether arguments are passed by value or
by reference, or whether there is a mix of both.
• In C, all function arguments are passed by value, i.e., they
are copied to their corresponding parameters.
• For Example,
– When c2f is called, the value of celsius is copied to f_celsius.
– Since a parameter resides in its own memory space, celsius and
f_celsius occupy separate memory locations.
– You can’t subsequently change celsius by changing f_celsius,
i.e., you can’t change an argument by changing its copy, the
parameter.
• It is thus not necessary to maintain separate names for
arguments and parameters in the declaration, definition
and invocation
2/11/2021 3.2 Functions 61

Passing by Reference
• Unlike C++, C doesn’t support passing by reference, where
both argument and parameter occupy the same memory
location.
• However, in C, a variable (p) can store the memory address
of another variable (x), and you can use p to indirectly
change the value of x.
• When a function is called, its arguments are copied to the
parameters.
• But if the function changes a parameter, then the change
is not seen in the caller.
• However, if an argument contains the address of a
variable, then the corresponding parameter of the
argument can be used to change that variable.
2/11/2021 3.2 Functions 62

Local Variables
• A function has its own set of local variables that are defined in its
implementation.
• For instance, the c2f function uses a local variable, fheit, to compute the
result it returns to its caller.
• Unlike parameters, local variables cannot be assigned by the caller.
• parameters and local variables have the following features:
– Their names don’t conflict with identical names defined in the caller or any
other function.
– They can be accessed only in the function they are defined in.
– They are neither visible in the caller nor in any other function.
– They last as long as the function is active. This means that they are created
every time the function is called.
• since main is the first function to be called and the last to terminate, its
variables have a longer lifetime compared to variables and parameters of
other functions.
• To reinforce our point, usage of identical variable names (Ex: x, y and
temp) in both calling and called function will create a problem.
2/11/2021 3.2 Functions 63

The “Problem” with Local Variables
2/11/2021 3.2 Functions 64

USING ARRAYS IN FUNCTIONS
• Functions also use arrays as arguments.
• You can pass both an individual array element
and the name of an array as argument to a
function.
• The principles of parameter passing apply to
arrays too, but they affect array elements and
entire arrays in opposite ways.
2/11/2021 3.2 Functions 66

Passing an Array as an Argument
2/11/2021 3.2 Functions 67

PASSING A TWO-DIMENSIONAL ARRAY AS ARGUMENT
• A function can also work with the name of a 2D array as an
argument.
• Like with a 1D array, a 2D array is specified differently in the
declaration (and definition) and invocation.
• In the former case, you may drop the first subscript (rows),
but you can’t drop the second subscript (columns).
• Without knowledge of the number of columns, it would be
impossible for the compiler to know when one row ends
and another begins, considering that the rows are placed
next to one another in memory.
2/11/2021 3.2 Functions 68

CALLING A FUNCTION FROM ANOTHER FUNCTION
• Just as main calls a function, a function can
also call another function.
• The called function can in turn call another
function, an
• The remaining functions then return in the
reverse sequence of their invocation.
• Ultimately, the outermost function returns
control to main.
2/11/2021 3.2 Functions 69

Contents
1. Arrays
2. Functions
5. Storage classes.
2/11/2021 72
3.2 Functions

RECURSIVE FUNCTIONS
• Loops use the iterative technique to repeatedly update
a set of data with the same set of instructions.
• Repetition can also be achieved by recursion, a form of
cloning that uses instructions to specify themselves.
• In C, a recursive function calls itself, which on return
delivers to its caller its share of the final solution.
• A recursive function must not be allowed to run
forever because the program will eventually run out of
memory.
2/11/2021 3.2 Functions 73

RECURSIVE FUNCTIONS
• Because the static variable count is defined and
initialized just once, it can track the number of calls
made to main.
• You are aware that function variables and parameters
are saved in a separate region of memory called the
stack.
• With every recursive call, the stack grows in size, and if
this growth goes unchecked, the stack will eventually
overflow.
• In this program, after main has called itself 523,172
times, stack overflow occurs and terminates the
program with a “segmentation fault.”
• This is not the way recursive functions are meant to
be used.
2/11/2021 3.2 Functions 75

Using a Recursive Function to Compute Factorial
• This is simply the product of all integers from 1 to
the number.
• For instance, 6!, the factorial of 6, is 6 × 5 × 4 × 3
× 2 × 1 = 720.
• But 6! can also be expressed as 6 × 5! in the same
way as 5! is expressed as 5 × 4!.
• We can thus express the factorial of a number in
this manner:
2/11/2021 3.2 Functions 76

VARIABLE SCOPE AND LIFETIME
• Apart from having a data type, a variable has space and time
attributes.
• The space attribute signifies the scope or visibility of the variable.
This is actually the region of the program where the variable is
visible and can be accessed.
• A variable may have one of four possible scopes: block, function,
file and program.
– A variable having block scope is visible in the block in which it is
declared.
– A variable having file scope is visible in the entire file.
• The time attribute determines the lifetime of the variable, i.e., its
time of birth and death.
• A variable declared inside a function lives as long as the function is
active. One declared before main is alive for the duration of the
program.
2/11/2021 3.2 Functions 78

Local and Global Variables
• Variables declared inside a function are visible
only in the function. They have local scope, the
reason why they are called local variables.
• Variables declared outside a function are known
as global variables. The scope of a global variable
extends from the point of its declaration to the
rest of the file.
• When a variable is declared before main, it is
truly global across the entire program (which
may be spread across multiple files).
2/11/2021 3.2 Functions 79

Scope of Global and Local Variables
2/11/2021 3.2 Functions 80

Variable Hiding
2/11/2021 3.2 Functions 81

THE STORAGE CLASSES
• The scope, lifetime and initial value of a variable
are determined by its storage class.
• So far, we have used the default storage class for
variables (automatic), but you also need to know
the following storage classes supported by C:
– automatic (auto)
– static (static)
– external (extern)
– register (register)
• The storage class also determines the way the
compiler allocates memory for a variable.
2/11/2021 3.2 Functions 82

Static Variables (static)
• If a local variable is assigned the static storage
class, then it will retain its value between
function calls.
• A static variable (keyword: static) is created
and initialized just once, when the function
containing its declaration is executed.
2/11/2021 3.2 Functions 84

External Variables (extern)
• A global or external variable is defined outside a
function and is visible everywhere—even in other files
that constitute the program.
2/11/2021 3.2 Functions 85

Register Variables (register)
• All program variables are stored in primary memory which is faster
than disk but slower then registers directly connected to the CPU.
• The register storage class (keyword: register) permits a variable to
be stored in one of the high-speed CPU registers.
• The compiler will attempt to store the variable x in one of the
registers, failing which it will use primary memory.
• A register normally has a size of one word, not all variables can be
assigned this storage class.
• Generally, register is restricted to char and int variables.
• However, you can’t obtain the address of a register variable using
&x because registers don’t use the addressing system used by
primary memory.
2/11/2021 3.2 Functions 86

Thank you
2/11/2021 3.2 Functions 87

C Programming : Recursive Functions,
Variable Scope and Lifetime and
Storage Classes
By
Mr.S.Selvaraj

Contents
1. Arrays
2. Functions
5. Storage classes.
2/11/2021 89
3.3 Recursive Functions

RECURSIVE FUNCTIONS
• Loops use the iterative technique to repeatedly update
a set of data with the same set of instructions.
• Repetition can also be achieved by recursion, a form of
cloning that uses instructions to specify themselves.
• In C, a recursive function calls itself, which on return
delivers to its caller its share of the final solution.
• A recursive function must not be allowed to run
forever because the program will eventually run out of
memory.
2/11/2021 3.3 Recursive Functions 90

RECURSIVE FUNCTIONS
• Because the static variable count is defined and
initialized just once, it can track the number of calls
made to main.
• You are aware that function variables and parameters
are saved in a separate region of memory called the
stack.
• With every recursive call, the stack grows in size, and if
this growth goes unchecked, the stack will eventually
overflow.
• In this program, after main has called itself 523,172
times, stack overflow occurs and terminates the
program with a “segmentation fault.”
• This is not the way recursive functions are meant to
be used.

Using a Recursive Function to Compute Factorial
• This is simply the product of all integers from 1 to
the number.
• For instance, 6!, the factorial of 6, is 6 × 5 × 4 × 3
× 2 × 1 = 720.
• But 6! can also be expressed as 6 × 5! in the same
way as 5! is expressed as 5 × 4!.
• We can thus express the factorial of a number in
this manner:

VARIABLE SCOPE AND LIFETIME
• Apart from having a data type, a variable has space and time
attributes.
• The space attribute signifies the scope or visibility of the variable.
This is actually the region of the program where the variable is
visible and can be accessed.
• A variable may have one of four possible scopes: block, function,
file and program.
– A variable having block scope is visible in the block in which it is
declared.
– A variable having file scope is visible in the entire file.
• The time attribute determines the lifetime of the variable, i.e., its
time of birth and death.
• A variable declared inside a function lives as long as the function is
active. One declared before main is alive for the duration of the
program.

Local and Global Variables
• Variables declared inside a function are visible
only in the function. They have local scope, the
reason why they are called local variables.
• Variables declared outside a function are known
as global variables. The scope of a global variable
extends from the point of its declaration to the
rest of the file.
• When a variable is declared before main, it is
truly global across the entire program (which
may be spread across multiple files).

Scope of Global and Local Variables

Variable Hiding

THE STORAGE CLASSES
• The scope, lifetime and initial value of a variable
are determined by its storage class.
• So far, we have used the default storage class for
variables (automatic), but you also need to know
the following storage classes supported by C:
– automatic (auto)
– static (static)
– external (extern)
– register (register)
• The storage class also determines the way the
compiler allocates memory for a variable.

Static Variables (static)
• If a local variable is assigned the static storage
class, then it will retain its value between
function calls.
• A static variable (keyword: static) is created
and initialized just once, when the function
containing its declaration is executed.

External Variables (extern)
• A global or external variable is defined outside a
function and is visible everywhere—even in other files
that constitute the program.

Register Variables (register)
• All program variables are stored in primary memory which is faster
than disk but slower then registers directly connected to the CPU.
• The register storage class (keyword: register) permits a variable to
be stored in one of the high-speed CPU registers.
• The compiler will attempt to store the variable x in one of the
registers, failing which it will use primary memory.
• A register normally has a size of one word, not all variables can be
assigned this storage class.
• Generally, register is restricted to char and int variables.
• However, you can’t obtain the address of a register variable using
&x because registers don’t use the addressing system used by
primary memory.

Thank you

C Programming : Arrays and Functions

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