second session of C-programming workshop

1. With/Mohamed Fawzy
C-Programming Language-2015
1 Day #2

2. 2
Lecture Notes:
 Set your phone to vibration mode.
 Ask any time.
 During labs feel free to check any materials or internet.

3. Contents
3
Arrays.
Control statements.
Pointers.
Functions.
Dynamically memory allocation

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Arrays.
 which can store a fixed-size sequential collection of elements of the
same type.
 All arrays consist of contiguous memory locations (Single Block).
 The size of array, once declared, is fixed and cannot be modified.
 Single Dimension Array.
 Multi Dimension Array (Array of Arrays).
EX:
char a[5]; //Array of 5 characters.
EX:
char a[3][4];
/*Array of three arrays
and each array has 4 characters.*/

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Examples:
double d[100]={1.5,2.7};
//first two elements initialized and remaining ones set to zero.
short num[]={1,2,3,4,5,6};
//compiler fixes size at 7 elements.
short num[]={1,2,3,4,5,6};
//compiler fixes size at 7 elements.

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Take Care !!!!
#define size 10
int a[size];
char size=10;
int a[size];
const char size=10;
int a[size];
int a[5.3];
//size must be an integer
int a[5];
a[5]=50;
//in this case it will overwrite some data.
a[-1]=5;
//the index must be an integer.

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Control Statements.
 For Statements.
for (initial value;condition;update)
{
//statements
}
OR
initial value;
for(;condition;)
{
//statements
update;
}

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Take Care !!!!
char x;
for(x=0;x<200;x++)
{
printf(“c programming”);
}
for(;;)
{
printf(“c programming”);
}

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 while loop.
while (condition)
{
//statements
}
 do while loop.
do
{
//statements
}
while (condition)
Control Statements.

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Break & Continue.
• Break and continue are used to modify the execution of loops.
 break.
When the break statement is encountered inside a loop, the loop is immediately
terminated and program control resumes at the next statement following the loop.
 Continue.
continue forces the next iteration of the loop to take place, skipping
any code in between.

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Examples:
//program to print even numbers between(0:50)
int main()
{
char x=0;
while (x<=50)
{
if(x%2){
x++;
continue;
}
printf("%dn",x++);
}
return 0;
}

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Pointers.
Why pointers?
• Achieve call by reference with functions.
• Arrays and structures are difficult without pointers.
• Create linked list, trees and graph.
Note:
We must take care in using pointers since, there are no safety features.

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Declaring pointers.
• Pointers are declared using “*”.
Int x; //declaring an integer
Int* x; //declaring pointer to an integer
char* m; //declare pointer to character
Notes:
• Pointers may only point to variables of the same type as the pointer
has been declared.
• A pointer to an int may only point to int.
• A pointer to a double may only point to double not float or long double.
• (&) stands for “address of….”
• (*) stands for “content of…”

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Example:

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Take Care !!!!

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Pointers and arrays.
• The name of array is a pointer to the 0th place of array.
• You cannot apply increment or decrement on array name.
• Pointer is useful for passing array to function and safe stack memory.
EX#1:
double *ptr;
double arr[10];
Ptr=arr; //ptr=&arr[0]
arr++; //not allowed
ptr++; //allowed
EX#2:
void print_arr(char *ptr){
printf(“%dn”,*(ptr++));
}
. . . . . . . . . . .
char arr[10];
Print_arr(arr);
Take Care !!!!
char *ptr[5]; //array of five pointers to char
char (*ptr)[5]; //pointer to array of 5 elements

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EX#3:
char (*ptr)[5];
char arr[5] {5,6,7,8,9};
Ptr=arr;
ptr++;
5
0
1
2
3
4
5
6
7
8
9
Garbage value

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Functions.
• Functions are blocks of code that perform a number of pre-defined commands to
accomplish something productive. You can either use the built-in library functions
or you can create your own functions.
• Functions that a programmer writes will generally require a prototype.
• It tells the compiler what the function will return, what the function will be called,
as well as what arguments the function can be passed.
return-type <function-name> (arg_type arg1, arg_type arg2,…);
Exs.
void fun (void); //function which take nothing and return nothing
void fun (int x,int y,…); //function take arguments and return nothing
int fun (void); //function take nothing and return int
int fun (int x,int y,…); //function take arguments and return int

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Ex#1.
#include <stdio.h>
int mult ( int x, int y ); //prototype of function
int main()
{
int x,int y,int result;
printf( "Please input two numbers to be multiplied: " );
scanf( "%d", &x );
scanf( "%d", &y );
result= mult(x,y); //calling the function
printf( "The product of two numbers is %dn",result);
return 0;
}
//implementation of function
int mult (int x, int y)
{
return x * y;
}
Functions. cont‟d
Pointer to function.

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What happened in calling function?
Save some data in memory segment called stack.
• the value of PC (Program Counter).
• A copy of parameters passed to function.
• The value which returned from function.
Note:
If size of data stored on stack is larger than whole stack size it will cause
Common error called “Stack Overflow”.
Problem:
What if we need to pass a huge data to function to be processed.
Solution:
We can pass by reference because any pointer only occupy 4 bytes.
Functions. cont‟d
Calling function.

21. 21
Write a c program to calculate the largest number in passed array.
#include <studio.h>
char calc_largest (char *ptr,char siz)
{
char largest=*ptr;
char i=0;
for (i=0;i<siz;i++)
{
if (*(ptr+i) >largest)
largest=*(ptr+i);
else
continue;
}
return largest;
}
int main(){
char arr[]={45,12,5,44,6,8,60}
printf(“the largest value is %d”,calc_largest(arr,sizeof(arr));
}
Functions. cont‟d

22. 22
Functions. cont‟d
Pointer to function.
• Pointer to function allow programmers to pass a function as a
parameter to another function.
• Function pointer syntax.
<return data_type> (* pointer_name)(arguments passed to function);
EX#1:
void (*ptr)(int arg1,int arg2);
/*
Pointer to function which return nothing and take two
integers parameters.
*/
Note:
Don't be confused between pointer to function and pointer to array.

23. 23
Functions. cont‟d
Initializing Pointer to function.
EX#2:
void my_int_func(int x)
{
printf( "%dn", x );
}
int main()
{
void (*ptr)(int);
/* the ampersand is actually optional */
ptr = &my_int_func;
(*ptr)( 2 ); //or ptr(2);
return 0;
}

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Hands ON

25. Email: mo7amed.fawzy33@gmail.com
Phone: 01006032792
Facebook: mo7amed_fawzy33@yahoo.com
Contact me:
25

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