c type cast

7/28/2019 C type cast

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C type casting

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CTypecasting concept is used to modify a variable from one date type to another data type. New data type should be mentioned before the variable in brackets which to be type casted.

C Type casting Example program:

In the below program, 7/5 alone will produce integer value. So, type cast is done before division to retain float result.

C

// Structure using typedef:

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#include

int main (){

float x;

x = (float) 7/5;

printf("%f",x);

Output:

1.400000

It is best practice to convert lower data type to higher data type to avoid data loss. Data will be truncated when higher data type is converted to lower. For example, if float is converted to int, data which is present after decimal

point will be lost.

Inbuilt typecast functions:

There are many inbuilt typecast functions available in C language which performs data type conversion from one type to another. They are

given in below table. Click on each function name to display an example program.S.no Function Description

1 atof Converts string to float

2 atoi Converts string to int

3 atol Converts string to long

4 itoa Converts int to string

5 ltoa Converts long to string
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Example program for atof():

It converts string to float data type.

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#include

#include

int main()

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#include

#include

int main()

{

char a[10] = "3.14";float pi = atof(a);

printf("Value of pi = %f\n", pi);

return 0;

}Output:

Value of pi = 3.140000

Example program for atoi():

It converts string to int data type.

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#include

#include

int main(){

char a[10] = "100";

int value = atoi(a);

printf("Value = %d\n", value);return 0;


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10 }Output:

Value = 100

Example program for atol():

It converts string to long data type.

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#include

#include

#include

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#include

#include

int main()

{

char a[20] = "100000000000";long value = atol(a);

printf("Value = %ld\n", value);

return 0;

}

Output:

Value = 100000000000

Example program for itoa():

It converts int to string data type.

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#include

#include #include

int main(){

int a=54325;char buffer[20];itoa(a,buffer,2); // here 2 means binary

printf("Binary value = %s\n", buffer);

itoa(a,buffer,10); // here 10 means decimalprintf("Decimal value = %s\n", buffer);

itoa(a,buffer,16); // here 16 means Hexadecimalprintf("Hexadecimal value = %s\n", buffer);


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return 0;}

Output:

Binary value = 1101010000110101

Decimal value = 54325

Hexadecimal value = D435Example program for ltoa():

It converts long to string data type.

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#include

#include

#include

int main()

{

long a=10000000;

char buffer[50];

ltoa(a,buffer,2); // here 2 means binary

printf("Binary value = %s\n", buffer);

ltoa(a,buffer,10); // here 10 means decimal

printf("Decimal value = %s\n", buffer);

ltoa(a,buffer,16); // here 16 means Hexadecimal

printf("Hexadecimal value = %s\n", buffer);

return 0;

}

Output:

Binary value = 100110001001011010000000

Decimal value = 10000000

Hexadecimal value = 989680

C typedef

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C- Typedef : It is a keyword that is used to give a new symbolic name for the existing name in a C program. This is same like defining alias for the commands. Consider the below structure

struct student

{

int mark [2];

char name [10];

float average;

};

Variable for the above structure can be declared in two ways.1st way :

struct student record; // for normal variable
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struct student *record; // for pointer variable

2nd way :

typedef struct student status;

When we use typedef keyword before struct like above, after that we can simply use type definition (here it is sta tus) in the C program to declare

structure variable.

Now, structure variable declaration will be, status record. This is equal to struct student record. Type definition for struct student is status.

i.e. status = struct student

C -typedef : An alternative way for structure declaration:

typedef struct student

{

int mark [2];

char name [10];

float average;

}status;

To declare structure variable, we can use the below statements.

status record1; //record 1 is structure variable

status record2; //record 2 is structure variable

Example program for C typedef :

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// Structure using typedef:

#include

#include

typedef struct student

{

int id;

char name[20];

float percentage;

} status;

int main(){

status record;

record.id=1;

strcpy(record.name, "Raju");

record.percentage = 86.5;

printf(" Id is: %d \n", record.id);

printf(" Name is: %s \n", record.name);

printf(" Percentage is: %f \n", record.percentage);

return 0;

}

Output:


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Id is: 1

Name is: Raju

Percentage is: 86.500000

Typedef can be used to simplify the rea l commands as per our need.For example,

typedef long long int LLI;

In above statement, LLI is the type definition for the real C command long long int. We can use type defini tion LLI instead of using full command long long int in

a C program once it is de fined.

Another example program for C typedef:

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#include

#include

int main()

{

typedef long long int LLI;

printf("Storage size for long long int data " \

"type : %ld \n", sizeof(LLI));

return 0;

}

Output:

Storage size for long long int data type : 8

C Command line arguments

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Command line arguments in C:

main() function of a C program accepts arguments from command line or from other shell scripts by following

commands. They are,

argc argv[]

where,

argc - number of arguments in the command line including program name

argv[] - This is carrying all the arguments .

In real time application, it will happen to pass arguments to the main program itself. These arguments arepassed to the main () function while executing binary file from command line.
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For example, when we compile a program (test.c), we get executable file in the name test. Now, we run the executable test along with 4 arguments in command line like below.

./test this is a program

Where,

argc = 5

argv[0] = test

argv[1] = this

argv[2] = is

argv[3] = a

argv[4] = program

argv[5] = NULL

Example program for argc() and argv() functions:

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#include

#include

int main(int argc, char *argv[]) // command line arguments

{

if(argc!=5)

{

printf("Arguments passed through command line " \

"not equal to 5");

return 1;}

printf("\n Program name : %s \n", argv[0]);

printf("1st arg : %s \n", argv[1]);

printf("2nd arg : %s \n", argv[2]);

printf("3rd arg : %s \n", argv[3]);

printf("4th arg : %s \n", argv[4]);

printf("5th arg : %s \n", argv[5]);


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return 0;

}

Output:

Program name : test

1st arg : this2nd arg : is

3rd arg : a

4th arg : program

5th arg : (null)

Do you know difference between int and void data type used in functions?

S.no int void

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int main ()

In the above statement, int means, this main

function returns a value of integer data type

to the calling function.

void main ()

In the above statement, void means, this

main function doesnt return any value to

the calling function.

2 int main () and int main (void) are same.void main () and void main (void) are

same.

3

int main (int argc, char + argv ())In the

above statement, arguments are passed to

the main function. Where,

argc no. of arguments passed.

agrv ()carries passed arguments. The

above function gets the argument from

command line and returns the integer value.

void main (int argc, char + argv ())This gets

arguments from command line. But,

doesnt return any value to calling function.

C Preprocessor directives

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CPreprocessor directives:

Before a C program is compiled in a compiler, source code is processed by a program called preprocessor. Thisprocess is called preprocessing.

Commands used in preprocessor are called preprocessor directives and they begin with # symbol. Below is the list of preprocessor directives that C language offers.

S.no Preprocessor Syntax Description

1 Macro #defineThis macro defines constant value and can be

any of the basic data types.

2Header file

inclusion#include

The source code of the file file_name is

included in the main program at the specified

place
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3Conditional

compilation#ifdef, #endif, #if,

#else, #ifndef

Set of commands are included or excluded in

source program before compilation with

respect to the condition

4 Other directives # undef#pragma

#undef is used to undefine a defined macro

variable.#Pragma is used to call a function

before and after main function in a C program

A program in C language involves into different processes. Below diagram will help you to understand all the

process that a C program comes across.

Example program for #define, #include C preprocessors:

#define - This macro defines constant value and can be any of the basic data types.#include - The

source code of the file file_name is included in the main program at the specified place

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#include

#define height 100

#define number 3.14

#define letter 'A'

#define letter_sequence "ABC"

#define backslash_char '\?'

void main()

{

printf("value of height : %d \n", height );

printf("value of number : %f \n", number );

printf("value of letter : %c \n", letter );

printf("value of letter_sequence : %s \n", letter_sequence);

printf("value of backslash_char : %c \n", backslash_char);

}

Output:

value of height : 100 value of number : 3.140000 value of letter : A value of letter_sequence : ABC

value of backslash_char : ?

Example program for conditional compilation directives:

a) Example program for #ifdef, #else and #endif:

#ifdef directive checks whether particular macro is defined or not. If it is defined, If clause statements are included

in source file. Otherwise, else clause statements are included in source file for compilation and execution.

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#include

#define RAJU 100

int main()

{

#ifdef RAJU

printf("RAJU is defined. So, this line will be added in " \"this C file\n");

#else

printf("RAJU is not defined\n");

#endif

return 0;

}

Output:


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RAJU is defined. So, this line will be added in this C file

b) Example program for #ifndef and #endif:

It exactly acts as reverse as #ifdef directive. If particular macro is not defined, If clause statements are included in

source file. Otherwise, else clause statements are included in source file for compilation and execution.

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#include

#define RAJU 100

int main()

{#ifndef SELVA

{

printf("SELVA is not defined. So, now we are going to " \

"define here\n");

#define SELVA 300

}

#else

printf("SELVA is already defined in the program);

#endif

return 0;

}Output:

SELVA is not defined. So, now we are going to define here

c) Example program for #if, #else and #endif:

If clause statement is included in source file if given condition is true. Otherwise, else clause statement is included in

source file for compilation and execution.

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#define a 100


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int main()

{

#if (a==100)

printf("This line will be added in this C file since " \

"a \= 100\n");

#else

printf("This line will be added in this C file since " \"a is not equal to 100\n");

#endif

return 0;

}

Output:

This line will be added in this C file since a = 100

Example program for undef:

This directive undefines existing macro in the program.

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#include

#define height 100

void main()

{printf("First defined value for height : %d \n", height );

#undef height // undefining variable

#define height 600 // redefining the same for new value

printf("value of height after undef \& redefine:%d",height);

}

Output:

First defined value for height : 100 value of height after undef & redefine:600

Example program for pragma:

Pragma is used to call a function before and after main function in a C program

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#include

void function1( );

void function2( );

#pragma startup function1

#pragma exit function2

int main( )

{

printf ( "\n Now we are in main function" ) ;

return 0;

}

void function1( )

{

printf("\nFunction1 is called before main function call");

}

void function2( )

{

printf ( "\nFunction2 is called just before end of " \

"main function" ) ;"

}

Output:

Function1 is called before main function call

Now we are in main function

Function2 is called just before end of main function

More on pragma directive:

S.no Pragma command description

1#Pragma startup

This directive executes function named

function_name_1 before

2#Pragma exit

This directive executes function named

function_name_2 just before termination of the program

3 #pragma warnrvlIf function doesnt return a value, then warnings are

suppressed by this directive while compiling.

4 #pragma warnparIf function doesnt use passed function parameter , then

warnings are suppressed

5 #pragma warnrch If a non reachable code is written inside a program, suchwarnings are suppressed by this directive.

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C Dynamic memory allocation

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C - Dynamic Memory Allocation:
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The process of allocating memory during program execution is called dynamic memory allocation.

CDynamic memory allocation functions:

C language offers 4 dynamic memory allocation functions. They are,

1. malloc()2. calloc()3. realloc()4. free()

S.no Function Syntax

1 malloc () malloc (number *sizeof(int));

2 calloc () calloc (number, sizeof(int));

3realloc ()

realloc (pointer_name, number * sizeof(int));

4 free () free (pointer_name);

malloc ():

malloc () function is used to allocate space in memory during the execution of the program. malloc () does not initialize the memory allocated during execution. It carries garbage value. malloc () function returns null pointer if it couldnt able to allocate requested amount of memory.

Example program for malloc() in C:

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#include

#include

#include

int main()

{

char *mem_allocation;/* memory is allocated dynamically */

mem_allocation = malloc( 20 * sizeof(char) );

if( mem_allocation== NULL )

{

printf("Couldn't able to allocate requested memory\n");

}

else

{


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strcpy( mem_allocation,"fresh2refresh.com");

}

printf("Dynamically allocated memory content : " \

"%s\n", mem_allocation );

free(mem_allocation);

}

Output:

Dynamically allocated memory content : fresh2refresh.com

calloc ()

calloc () function is also like malloc () function. But calloc () initializes the allocated memory to zero. But,malloc() doesnt.

Example program for calloc() in C:

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#include

#include

#include

int main()

{

char *mem_allocation;/* memory is allocated dynamically */

mem_allocation = calloc( 20, sizeof(char) );

if( mem_allocation== NULL )

{


}

else

{


}



free(mem_allocation);}

Output:


realloc ()


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realloc () function modifies the allocated memory size by malloc () and calloc () functions to new size. If enough space doesnt exist in memory of current block to extend, new block is allocated for the full size of

reallocation, then copies the existing data to new block and then frees the old block.

free ():

free () function frees the allocated memory by malloc (), calloc (), realloc () functions and returns the memoryto the system.

Example program for realloc() and free():

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#include

#include

#include

int main()

{

char *mem_allocation;

/* memory is allocated dynamically */

mem_allocation = malloc( 20 * sizeof(char) );

if( mem_allocation == NULL )

{


}else

{


}



mem_allocation=realloc(mem_allocation,100*sizeof(char));

if( mem_allocation == NULL )

{


}

else

{

strcpy( mem_allocation,"space is extended upto " \

"100 characters");

}

printf("Resized memory : %s\n", mem_allocation );

free(mem_allocation);

}

Output:


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Resized memory : space is extended upto 100 characters

Do you know difference betweenStatic memory allocation and Dynamic memory

allocation?

S.no Static memory allocationDynamic memory allocation

1

In static memory allocation, memory is

allocated while writing the C program.

Actually, user requested memory will be

allocated at compile time.

In static memory allocation, memory

is allocated while executing the

program. That means at run time.

2Memory size cant be modified while

execution.Example: array

Memory size can be modified while

execution.Example: Linked list

Do you know difference between malloc and calloc?

S.no malloccalloc

1It allocates only single block of requested

memory

It allocates multiple blocks of requested

memory

2

int *ptr;ptr = malloc( 20 * sizeof(int) );For

the above, 20*4 bytes of memory only

allocated in one block.

Total = 80 bytes

int *ptr;Ptr = calloc( 20, 20 * sizeof(int)

);For the above, 20 blocks of memory

will be created and each contains 20*4

bytes of memory.

Total = 1600 bytes

3malloc () doesnt initializes the allocated

memory. It contains garbage values

calloc () initializes the allocated memory

to zero

4

type cast must be done since this function

returns void pointerint *ptr;ptr =

(int*)malloc(sizeof(int)*20 );

Same as malloc () functionint *ptr;ptr =

(int*)calloc( 20, 20 * sizeof(int) );

C int, char validation

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The functions used to validate the data type of the given variable are given below with description and

example programs. These are all the inbuilt functions in C language.

S.no Function Description

1 isalpha checks whether character is alphabetic

2 isdigit checks whether character is digit

3 isalnum checks whether character is alphenumeric
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4 isspace checks whether character is space

5 islower checks whether character is lower case

6 isupper checks whether character is upper case

7 isxdigit checks whether character is hexadecimal

8 tolowerchecks whether character is alphabetic and

converts to lower case

9 toupperchecks whether character is alphabetic and

converts to upper case

Example program for isalpha():

This function checks whether character is alphabetic

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#include

int main()

{

char ch;

printf("Enter any character\n");

scanf("%c", &ch);if ( isalpha ( ch ) )

printf ( "\nEntered character is alphabetic" ) ;

else

printf ( "\nEntered character is not alphabetic" ) ;

}

Output:

Example

program

for

isdigit():

This function checks whether character is digit

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Enter any character

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Entered character is not alphabetic


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#include

int main()

{

char ch;


scanf("%c", &ch);

if ( isdigit ( ch ) )

printf ( "\nEntered character is digit" ) ;

else

printf ( "\nEntered character is not digit" ) ;

}

Output:

Enter any character

200

Entered character is digit

Example program for isalnum():

This function checks whether character is alphenumeric

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#include

int main()

{

char ch;


scanf("%c", &ch);

if ( isalnum ( ch ) )

printf ( "\nEntered character is alphanumeric" ) ;

else

printf ( "\nEntered character is not alphanumeric" ) ;

}

Output:


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Enter any character

@

Entered character is not alphanumeric

Example program for isspace():

This function checks whether character is space

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#include

int main()

{

char ch;


scanf("%c", &ch);

if ( isspace ( ch ) )

printf ( "\nEntered character is space" ) ;

else

printf ( "\nEntered character is not space" ) ;

}

Output:

Enter any character

a

Entered character is not space

Example program for islower():

This function checks whether character is lower case

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#include

int main()

{

char ch;


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scanf("%c", &ch);

if ( islower ( ch ) )

printf ( "\nEntered character is lower case character") ;

else

printf("\nEntered character is not lower case character");}

Output:

Enter any character

a

Entered character is lower case character

Example program for isupper():

This function checks whether character is upper case

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#include

int main()

{

char ch;

printf("Enter any character\n");scanf("%c", &ch);

if ( isupper ( ch ) )

printf ( "\nEntered character is upper case character") ;

else

printf("\nEntered character is not upper case character");

}

Output:

Enter any character

A

Entered character is upper case character

Example program for isxdigit():

This function checks whether character is hexadecimal

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#include

int main()

{

char ch;


scanf("%c", &ch);

if ( isxdigit ( ch ) )

printf ( "\nEntered character is hexadecimal" ) ;

else

printf ( "\nEntered character is not hexadecimal" ) ;

}

Output:

Enter any character

#

Entered character is not hexadecimal

Example program for tolower():

This function checks whether character is alphabetic and converts to lower case

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#include

int main()

{

char ch;


scanf("%c", &ch);

if(isalpha(ch))

printf ( "\nEntered character is converted into " \

"lower character : %c\n",tolower ( ch ) ) ;

else

printf("Entered character is not an alphabetic");

}

Output:


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Enter any character

A

Entered character is converted into lower character : a

Example program for toupper():

This function checks whether character is alphabetic and converts to upper case

C

1

2

34

5

6

7

8

9

10

11

12

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14

#include

int main(){

char ch;


scanf("%c", &ch);

if(isalpha(ch))

printf ( "\nEntered character is converted into " \

"upper character : %c\n",toupper ( ch ) ) ;"

else

printf("Entered character is not an alphabetic");

}

Output:

Enter any character

a

Entered character is converted into upper character : A

c type cast

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