![C ProgrammingNotes
Prof. K. Adisesha 16
Here, operators with the highest precedence appear at the top of the table, those with the lowest
appear at the bottom. Within an expression, higher precedence operators will be evaluated first.
Show Examples
Category Operator Associativity
Postfix () [] -> . ++ - - Left to right
Unary + - ! ~ ++ - - (type)* & sizeof Right to left
Multiplicative * / % Left to right
Additive + - Left to right
Shift << >> Left to right
Relational < <= > >= Left to right
Equality == != Left to right
Bitwise AND & Left to right
Bitwise XOR ^ Left to right
Bitwise OR | Left to right
Logical AND && Left to right
Logical OR || Left to right
Conditional ?: Right to left
Assignment = += -= *= /= %=>>= <<= &= ^= |= Right to left
Comma , Left to right
C - Decision Making
Decision making structures require that the programmer specifies one or more conditions to be
evaluated or tested by the program, along with a statement or statements to be executed if the
condition is determined to be true, and optionally, other statements to be executed if the condition
is determined to be false.
Show below is the general form of a typical decision making structure found in most of the
programming languages −](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-16-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 25
Instead of declaring individual variables, such as number0, number1, ..., and number99, you
declare one array variable such as numbers and use numbers[0], numbers[1], and ..., numbers[99]
to represent individual variables. A specific element in an array is accessed by an index.
All arrays consist of contiguous memory locations. The lowest address corresponds to the first
element and the highest address to the last element.
Declaring Arrays
To declare an array in C, a programmer specifies the type of the elements and the number of
elements required by an array as follows −
type arrayName [ arraySize ];
This is called a single-dimensional array. The arraySize must be an integer constant greater than
zero and type can be any valid C data type. For example, to declare a 10-element array
called balance of type double, use this statement −
double balance[10];
Here balance is a variable array which is sufficient to hold up to 10 double numbers.
Initializing Arrays
You can initialize an array in C either one by one or using a single statement as follows −
double balance[5] = {1000.0, 2.0, 3.4, 7.0, 50.0};
The number of values between braces { } cannot be larger than the number of elements that we
declare for the array between square brackets [ ].
If you omit the size of the array, an array just big enough to hold the initialization is created.
Therefore, if you write −
double balance[] = {1000.0, 2.0, 3.4, 7.0, 50.0};
You will create exactly the same array as you did in the previous example. Following is an example
to assign a single element of the array −
balance[4] = 50.0;
The above statement assigns the 5th
element in the array with a value of 50.0. All arrays have 0 as
the index of their first element which is also called the base index and the last index of an array
will be total size of the array minus 1. Shown below is the pictorial representation of the array we
discussed above −](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-25-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 26
Accessing Array Elements
An element is accessed by indexing the array name. This is done by placing the index of the
element within square brackets after the name of the array. For example −
double salary = balance[9];
The above statement will take the 10th
element from the array and assign the value to salary
variable. The following example Shows how to use all the three above mentioned concepts viz.
declaration, assignment, and accessing arrays −
#include <stdio.h>
int main () {
int n[ 10 ]; /* n is an array of 10 integers */
int i,j;
/* initialize elements of array n to 0 */
for ( i = 0; i < 10; i++ ) {
n[ i ] = i + 100; /* set element at location i to i + 100 */
}
/* output each array element's value */
for (j = 0; j < 10; j++ ) {
printf("Element[%d] = %dn", j, n[j] );
}
return 0;
}
When the above code is compiled and executed, it produces the following result −
Element[0] = 100
Element[1] = 101
Element[2] = 102
Element[3] = 103
Element[4] = 104
Element[5] = 105
Element [6] = 106
Element [7] = 107
Element [8] = 108
Element [9] = 109
Arrays in Detail
Arrays are important to C and should need a lot more attention. The following important concepts
related to array should be clear to a C programmer –
Sr.No. Concept & Description
1 Multi-dimensional arrays
C supports multidimensional arrays. The simplest form of the multidimensional array is
the two-dimensional array.
2 Passing arrays to functions](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-26-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 27
You can pass to the function a pointer to an array by specifying the array's name without
an index.
3 Return array from a function
C allows a function to return an array.
4 Pointer to an array
You can generate a pointer to the first element of an array by simply specifying the array
name, without any index.
C - Pointers
Pointers in C are easy and fun to learn. Some C programming tasks are performed more easily
with pointers, and other tasks, such as dynamic memory allocation, cannot be performed without
using pointers. So it becomes necessary to learn pointers to become a perfect C programmer. Let's
start learning them in simple and easy steps.
As you know, every variable is a memory location and every memory location has its address
defined which can be accessed using ampersand (&) operator, which denotes an address in
memory. Consider the following example, which prints the address of the variables defined −
#include <stdio.h>
int main ()
{
int var1;
char var2[10];
printf("Address of var1 variable: %xn", &var1 );
printf("Address of var2 variable: %xn", &var2 );
return 0;
}
When the above code is compiled and executed, it produces the following result −
Address of var1 variable: bff5a400
Address of var2 variable: bff5a3f6
Pointers
A pointer is a variable whose value is the address of another variable, i.e., direct address of the
memory location. Like any variable or constant, you must declare a pointer before using it to store
any variable address. The general form of a pointer variable declaration is −
type *var-name;
Here, type is the pointer's base type; it must be a valid C data type and var-name is the name of the
pointer variable. The asterisk * used to declare a pointer is the same asterisk used for
multiplication. However, in this statement the asterisk is being used to designate a variable as a
pointer. Take a look at some of the valid pointer declarations −
int *ip; /* pointer to an integer */
double *dp; /* pointer to a double */
float *fp; /* pointer to a float */
char *ch /* pointer to a character */](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-27-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 29
location. But by convention, if a pointer contains the null (zero) value, it is assumed to point to
nothing.
To check for a null pointer, you can use an 'if' statement as follows −
if(ptr) /* succeeds if p is not null */
if(!ptr) /* succeeds if p is null */
Pointers in Detail
Pointers have many but easy concepts and they are very important to C programming. The
following important pointer concepts should be clear to any C programmer –
Sr.No. Concept & Description
1 Pointer arithmetic: There are four arithmetic operators that can be used in pointers: ++,
--, +, -
2 Array of pointers: You can define arrays to hold a number of pointers.
3 Pointer to pointer: C allows you to have pointer on a pointer and so on.
4 Passing pointers to functions in C: Passing an argument by reference or by address enable
the passed argument to be changed in the calling function by the called function.
5 Return pointer from functions in C: C allows a function to return a pointer to the local
variable, static variable, and dynamically allocated memory as well.
C - Strings
Strings are actually one-dimensional array of characters terminated by a null character '0'. Thus a
null-terminated string contains the characters that comprise the string followed by a null.
The following declaration and initialization create a string consisting of the word "Hello". To hold
the null character at the end of the array, the size of the character array containing the string is one
more than the number of characters in the word "Hello."
char greeting[6] = {'H', 'e', 'l', 'l', 'o', '0'};
If you follow the rule of array initialization then you can write the above statement as follows −
char greeting[] = "Hello";
Following is the memory presentation of the above defined string in C/C++ −](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-29-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 30
Actually, you do not place the null character at the end of a string constant. The C compiler
automatically places the '0' at the end of the string when it initializes the array. Let us try to print
the above mentioned string −
#include <stdio.h>
int main ()
{
char greeting[6] = {'H', 'e', 'l', 'l', 'o', '0'};
printf("Greeting message: %sn", greeting );
return 0;
}
When the above code is compiled and executed, it produces the following result −
Greeting message: Hello
C supports a wide range of functions that manipulate null-terminated strings –
Sr.No. Function & Purpose
1 strcpy(s1, s2);
Copies string s2 into string s1.
2 strcat(s1, s2);
Concatenates string s2 onto the end of string s1.
3 strlen(s1);
Returns the length of string s1.
4 strcmp(s1, s2);
Returns 0 if s1 and s2 are the same; less than 0 if s1<s2; greater than 0 if s1>s2.
5 strchr(s1, ch);
Returns a pointer to the first occurrence of character ch in string s1.
6 strstr(s1, s2);
Returns a pointer to the first occurrence of string s2 in string s1.
The following example uses some of the above-mentioned functions −
#include <stdio.h>
#include <string.h>
int main () {
char str1[12] = "Hello";
char str2[12] = "World";
char str3[12];
int len ;
/* copy str1 into str3 */
strcpy(str3, str1);](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-30-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 31
printf("strcpy( str3, str1) : %sn", str3 );
/* concatenates str1 and str2 */
strcat( str1, str2);
printf("strcat( str1, str2): %sn", str1 );
/* total lenghth of str1 after concatenation */
len = strlen(str1);
printf("strlen(str1) : %dn", len );
return 0;
}
When the above code is compiled and executed, it produces the following result −
strcpy( str3, str1) : Hello
strcat( str1, str2): HelloWorld
strlen(str1) : 10
C - Structures
Arrays allow to define type of variables that can hold several data items of the same kind.
Similarly structure is another user defined data type available in C that allows to combine data
items of different kinds.
Structures are used to represent a record. Suppose you want to keep track of your books in a library.
You might want to track the following attributes about each book −
Title
Author
Subject
Book ID
Defining a Structure
To define a structure, you must use the struct statement. The struct statement defines a new data
type, with more than one member. The format of the struct statement is as follows −
struct [structure tag] {
member definition;
member definition;
...
member definition;
} [one or more structure variables];
The structure tag is optional and each member definition is a normal variable definition, such as
int i; or float f; or any other valid variable definition. At the end of the structure's definition, before
the final semicolon, you can specify one or more structure variables but it is optional.
Here is the way you would declare the Book structure −](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-31-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 32
struct Books {
char title[50];
char author[50];
char subject[100];
int book_id;
} book;
Accessing Structure Members
To access any member of a structure, we use the member access operator (.). The member access
operator is coded as a period between the structure variable name and the structure member that
we wish to access. You would use the keyword struct to define variables of structure type. The
following example shows how to use a structure in a program −
#include <stdio.h>
#include <string.h>
struct Books {
char title[50];
char author[50];
char subject[100];
int book_id;
};
int main( ) {
struct Books Book1; /* Declare Book1 of type Book */
struct Books Book2; /* Declare Book2 of type Book */
/* book 1 specification */
strcpy( Book1.title, "C Programming");
strcpy( Book1.author, "Nuha Ali");
strcpy( Book1.subject, "C Programming Tutorial");
Book1.book_id = 6495407;
/* book 2 specification */
strcpy( Book2.title, "Telecom Billing");
strcpy( Book2.author, "Zara Ali");
strcpy( Book2.subject, "Telecom Billing Tutorial");
Book2.book_id = 6495700;
/* print Book1 info */
printf( "Book 1 title : %sn", Book1.title);
printf( "Book 1 author : %sn", Book1.author);
printf( "Book 1 subject : %sn", Book1.subject);
printf( "Book 1 book_id : %dn", Book1.book_id);
/* print Book2 info */](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-32-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 33
printf( "Book 2 title : %sn", Book2.title);
printf( "Book 2 author : %sn", Book2.author);
printf( "Book 2 subject : %sn", Book2.subject);
printf( "Book 2 book_id : %dn", Book2.book_id);
return 0;
}
When the above code is compiled and executed, it produces the following result −
Book 1 title : C Programming
Book 1 author : Nuha Ali
Book 1 subject : C Programming Tutorial
Book 1 book_id : 6495407
Book 2 title : Telecom Billing
Book 2 author : Zara Ali
Book 2 subject : Telecom Billing Tutorial
Book 2 book_id : 6495700
C - Unions
A union is a special data type available in C that allows to store different data types in the same
memory location. You can define a union with many members, but only one member can contain
a value at any given time. Unions provide an efficient way of using the same memory location for
multiple-purpose.
Defining a Union
To define a union, you must use the union statement in the same way as you did while defining a
structure. The union statement defines a new data type with more than one member for your
program.
The format of the union statement is as follows −
union [union tag] {
member definition;
member definition;
...
member definition;
} [one or more union variables];
The union tag is optional and each member definition is a normal variable definition, such as int i;
or float f; or any other valid variable definition. At the end of the union's definition, before the
final semicolon, you can specify one or more union variables but it is optional. Here is the way
you would define a union type named Data having three members i, f, and str −
union Data {
int i;
float f;
char str[20];
} data;](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-33-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 34
Now, a variable of Data type can store an integer, a floating-point number, or a string of characters.
It means a single variable, i.e., same memory location, can be used to store multiple types of data.
You can use any built-in or user defined data types inside a union based on your requirement.
The memory occupied by a union will be large enough to hold the largest member of the union.
For example, in the above example, Data type will occupy 20 bytes of memory space because this
is the maximum space which can be occupied by a character string. The following example
displays the total memory size occupied by the above union −
#include <stdio.h>
#include <string.h>
union Data {
int i;
float f;
char str[20];
};
int main( ) {
union Data data;
printf( "Memory size occupied by data : %dn", sizeof(data));
return 0;
}
When the above code is compiled and executed, it produces the following result −
Memory size occupied by data : 20
Accessing Union Members
To access any member of a union, we use the member access operator (.). The member access
operator is coded as a period between the union variable name and the union member that we wish
to access. You would use the keyword union to define variables of union type. The following
example shows how to use unions in a program −
#include <stdio.h>
#include <string.h>
union Data {
int i;
float f;
char str[20];
};
int main( ) {
union Data data;
data.i = 10;
data.f = 220.5;
strcpy( data.str, "C Programming");
printf( "data.i : %dn", data.i);
printf( "data.f : %fn", data.f);
printf( "data.str : %sn", data.str);
return 0;
}](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-34-320.jpg)
![C ProgrammingNotes
Prof. K. Adisesha 35
When the above code is compiled and executed, it produces the following result −
data.i : 1917853763
data.f : 4122360580327794860452759994368.000000
data.str : C Programming
Here, we can see that the values of i and f members of union got corrupted because the final value
assigned to the variable has occupied the memory location and this is the reason that the value
of str member is getting printed very well.
Now let's look into the same example once again where we will use one variable at a time which
is the main purpose of having unions −
#include <stdio.h>
#include <string.h>
union Data {
int i;
float f;
char str[20];
};
int main( ) {
union Data data;
data.i = 10;
printf( "data.i : %dn", data.i);
data.f = 220.5;
printf( "data.f : %fn", data.f);
strcpy( data.str, "C Programming");
printf( "data.str : %sn", data.str);
return 0;
}
When the above code is compiled and executed, it produces the following result −
data.i : 10
data.f : 220.500000](/proxy?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fcprogrammingnotes-210306183140%2F85%2FC-programming-notes-35-320.jpg)
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Uploaded byProf. Dr. K. Adisesha
C programming notes
C programming is a general-purpose language developed in the 1970s to write operating systems like UNIX. It is one of the most widely used languages, particularly for systems programming. Some key facts: C was created to develop UNIX and is still widely used for operating systems, compilers, databases and other modern programs. It has various data types like integers, floats, characters, arrays and structures. Variables are defined with a data type and can be initialized. C code is written in files with a .c extension and preprocessed before compilation.
