C programming session5

C_Programming
Part 5
ENG. KEROLES SHENOUDA
1

3
The call a = calcm(5,6) works as follows:
1. Copies the values 5 and 6 to the variables x and y
2. Performs the internal calculations to calculate m
3. When executing the line (return m), the computer copies the value inside m and
return it to the line (a = calcm(5,6))
4. Copies the return value to (a) variable

Function Definition 4
Function Name: like variable, must have
no spaces and no special characters and
must starts
with letters
Input Parameters: supplied parameters
types and names. You can define any
number of
inputs; also you can define zero number of
inputs.
Return Type: the data type of the
function output, if the function has no
output use (void)
keyword.
Function Body: performs specific
function operation.
Return Statement: this statement tells
the computer that the function execution
is completed
and the required function output is ready
for the caller. The computer takes the
returned
value and supplies it to the caller.

C functions aspects syntax
function definition
Return_type
function_name (arguments
list)
{ Body of function; }
function call
function_name (arguments
list);
function declaration
return_type function_name
(argument list);
7

8
The compiler gives an error at the
line printWelcome(); in the
main function, the error
state that “the function
printWelcome is undefined”.
Which means that the compiler
cannot locate the function before the
main, even if it is located after the
main?

Calculate the Factorial
 Write a program uses a function to calculate the factorial of any positive
number
10

Lab:Calculate the Minimum Value of any
Given Array
int calcMin(int values[], int n) ;
12
Important: calcMin function takes two parameters an array and (int) value containing
the array size. Know that function could not expect the given array size, you must supply
it by yourself.

Finding a Name in a Set of Names
int findName(char names[][14], int n, char name[]);
14
void main()
{
char name[14];
char names[5][14] = {"Alaa", "Osama", "Mamdouh",
"Samy", "Hossain"};
puts("Enter your first name:");
gets(name);
if(findName(names, 5, name)==1)
puts("Welcome");
else
puts("Goodby");
}

Difference between Passing Single
Values and Arrays
15
This method copies the actual value of
an argument into the formal parameter
of the function. In this case, changes
made to the parameter inside the
function have no effect on the
argument.
This method copies the address of an
argument into the formal parameter. Inside
the function, the address is used to access
the actual argument used in the call. This
means that changes made to the parameter
affect the argument.

Write a program that produces
the following output:
23

What is memory layout of C-program ?
 when you run any C-program, its
executable image is loaded into RAM
 This memory layout is organized in
following fashion:
 Text segment
 Data segment
 Heap segment
 Stack segment
 Unmapped or reserved
24

Text segment
 Text segment contain executable instructions
of your C program, its also called code segment.
This is the machine language representation of
the program steps to be carried out, including
all functions making up the program, both user
defined and system
25

Data segment
 There are two sub section of this segment called initialized & uninitialized
data segment
 Initialized data:- It contains both static and global data that are initialized
with non-zero values.
 This segment can be further classified into read-only area and read-write area.
 For example : The global string defined by char string[ ] = “hello world” and a statement
like int count=1 outside the main (i.e. global) would be stored in initialized read-write
area. And a global statement like const int A=3 makes the variable ‘A’ read-only and to
be stored in initialized read-only area.
 Uninitialized data (bss segment):- Uninitialized data segment is also called BSS segment.
BSS stands for ‘Block Started by Symbol’ named after an ancient assembler operator.
Uninitialized data segment contains all global and static variables that are initialized to zero
or do not have explicit initialization in source code.
 For example : The global variable declared as int A would be stored in uninitialized data
segment. A statement like static int X=0 will also stored in this segment cause it
initialized with zero.
26

Heap segment
 The heap segment is area where dynamically allocated memory (allocated by
malloc(), calloc(), realloc() and new for C++) resides.
 When we allocate memory through dynamic allocation techniques(in simple
word, run time memory allocation), program acquire space from system and
process address space grows that’s why we saw upward arrow indication in
figure for Heap.
27

Stack segment
 The stack segment is area where local variables are stored. By saying local
variable means that all those variables which are declared in every function
including main( ) in your C program.
 When we call any function, stack frame is created and when function returns,
stack frame is destroyed including all local variables of that particular
function.
 Stack frame contain some data like return address, arguments passed to it,
local variables, and any other information needed by the invoked function.
 A “stack pointer (SP)” keeps track of stack by each push & pop operation
onto it, by adjusted stack pointer to next or previous address.
28

Local Variables 29
Above program have three functions each with
different scopes; each scope holds different
local variables. The variable a, b and c of main
function are inaccessible through myAdd or
myMull functions. The variables x, y and z of
myMull function are inaccessible through
myAdd or main functions, even if myAdd function
has the same variables names

Global Variables
 In the following program the variable
name is defined as a global variable, all
program
function can access this variable.
30

Static Variables
 Static variables are defined by the modifier static.
Static variables are initialized once in the
program life. For example if the variable (x) is
defined inside a function, the variable is
initialized only at first function call, further
function calls do not perform the initialization
step, this means that if the variable is modified by
any call the modification result remains
for the next call. Following example illustrate this
idea
31

Recursion
 Recursion is a situation happens
when a function calls itself directly
or indirectly.
34

Recursion
 Is recursion useful?
Recursion is an alternative way to
repeat the function execution with
the same or variant
parameters values. In another way
recursion is an indirect way to
make a loop; simply you
can convert any recursion to a
normal loop
35
Infinite Printing Loop

Recursion
 Is recursion useful?
Recursion is an alternative way to
repeat the function execution with
the same or variant
parameters values. In another way
recursion is an indirect way to
make a loop; simply you
can convert any recursion to a
normal loop
36
Finite Printing Loop

Follow Chapter 4/5:
Controlling Program
Flow
C PROGRAMMING FOR ENGINEERS, DR. MOHAMED SOBH
37The next Part we will talk about Variables Scope

References 38
 The Case for Learning C as Your First Programming Language
 A Tutorial on Data Representation
 std::printf, std::fprintf, std::sprintf, std::snprintf…..
 C Programming for Engineers, Dr. Mohamed Sobh
 C programming expert.
 fresh2refresh.com/c-programming
 Memory Layout of C Program

C programming session5

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