calloc

malloc

  There are 4 library routines calloc(), free(), alloc(),and malloc() which is used to allocate memory and free it up during the program execution Once when a memory space of specific size is allocated, it returns null pointer pointing to that allocated memory location.

  Calloc() initialized the allocated memory to zero Malloc() doesn’t initializes the allocated memory. It contains garbage Values It allocates multiple block of requested memory. It allocates only single block of requested memory.

Why use malloc()

• You can use malloc when you have to allocate objects which must exist beyond the execution of the memory block.
• Malloc can be used if we need to allocate memory greater than size of stack.
• Returns the pointer to the first byte of allocated space.
• Enables developers to allocate memory as it is needed in the exact amount.
• This function allocates memory block size bytes from the heap.

Syntax of malloc()

ptr = (cast_type *) malloc (byte_size); 

• In above syntax, ptr is a pointer of cast_type. Malloc function returns the pointer to the allocated memory of byte _size.

Example of malloc() in C

ptr = (int * ) malloc(50)

• When this statement is executed, malloc reserves a memory space of 50 bytes. The address of the first byte reserved space is assigned to the pointer

Why use calloc()

• When you have to set the allocated memory to 0.
• You can use calloc() that returns a pointer to get access to memory heap.
• Used when you need to initialize the elements to 0 to return a pointer to the memory.
• To prevent overflow that is possible with malloc()
• Use calloc() to request a page that is known to already be 0.

Syntax of Calloc()

ptr = (cast_type *) calloc (n, size); 

• The above syntax is used to allocate n memory blocks of the same size. After the memory space is allocated, all the bytes are initialized to zero. The pointer, which is currently at the first byte of the allocated memory space, is returned.

Constant

• A constant is a value or identifier whose value is fixed and does not change, in the entire program.
• Constant is similar to a variable but it can hold only a single variable during the execution of program.
• Ex: const double PI = 3.14;
  Here,
  • Const is a identifier
  • Double is a data type
  • PI is a constant variable name that takes a value of 3.14.
  • This value of 3.14 does not change during the entire program.

Variable

• Variable is any characteristic, number, or quantity that can be measured or counted.
• It is also called as data item.
• A Variable is a name or an identifier that can store any values, and those values can be changed at any time during the program.
• For example: int score = 6;
  • Here, score is a variable name of integer type that stores the value 6. The value of score can be changed any time during the program.

• Primary Data Types
• User Defined Data Types
• Secondary Data Types

Primary Data Types:

• Integer
• Float
• Char
• Double

User Defined Data Types:

• Structure
• Union
• Enum

Secondary Data Types:

• Array
• pointers

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Some commonly used data types are:

• char : char is a data type which stores single character. It needs one byte memory.
• Ex: char ch;
  • Here char is a data type that stores single character as its value.
  • Ch is variable name which stores the value of single character

• Int : integer is a data type that is used to store numerical numbers. It requires four-byte memory.
• Ex:int i;
  • Here int is a data type that stores numbers.
  • i is variable of type integers.

• Float: is a data type that is used to store decimal numbers with one decimal point. It also requires 4 byte of memory.
• Ex:float f;
  • Here float is a data type that stores decimal numbers with one decimal point. F is variable name.

• double: is a data type that is used to store decimal numbers with two decimal point.
• Ex:double d;
  • Here  double is a data type to store decimal value with two points.
  • d is a variable name.

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getc()

• This function gets single character as input and returns an integer value. If this fails, it returns EOF.

Syntax of getc()

int getc(FILE *stream);

getchar()

• The function getchar() reads the character from the standard input while getc() reads from the input stream.

 Syntax of getchar() 

  int getchar(void);

getch()

• The function getch() is a non-standard function.
• It is included in “conio.h” header file.
• Getch() is not a part of standard library.
• It returns the entered character without even waiting for the enter key.

  Syntax of getch()

int getch();

getche()

• Like getch(), the getche() function is also a non-standard function and is included in “conio.h” header file.
• It reads a single character from the keyboard and returns it immediately without even waiting for enter key.

 Syntax of getche()

int getche(void);

• L value or locator value represents an object that occupies some identifiable location in memory.
• In an assignment operator the l value can appear on right hand side or left hand side.
• Expression which refer to modifiable locations are called as “Modifiable L Values”.
• An incomplete type or constant attribute cannot have an array type of modifiable value attribute.
• Structures and Unions to be a modified lvalues, they should not contain any members with constant attribute.
• Storage location will be denoted by an identifier with name,value stored at a location will have the value of the variable.
• A lvalue identifier can be modified it refers to a memory location and if the type of it is arithmetic, structure, union or pointer.
• Example: If a pointer points to a storage region, then *ptr is a modifiable l value that allocates the storage region to which *ptr points.
• In C, this concept was termed “Locator Value”. And referred to expressions that locate objects.

The l-value is one of the following

• The name of the variable of any type i.e, an identifier of integral, floating, pointer, structure, or union type.
• A subscript ([ ]) expression that does not evaluate to an array.
• A unary-indirection (*) expression that does not refer to an array
• An l-value expression in parentheses.
• A constobject (a nonmodifiable l-value).
• The result of indirection through a pointer, provided that it isn’t a function pointer.
• The result of member access through pointer(-> or .)

R Value

• R- value refer to data value that is stored at some address in memory.
• R value is an expression that does not have a value assigned to it which means r value can either right side or left side of an assignment operator.

• This statement is used with switch statement.
• Can also be used with while loop, do – while loop and for loop.
• When the control encounters a break statement, the control will terminate the loop immediately and the statements after break will not be executed.

Syntax

Sample Code

#include<stdio.h>
int main()
{
  
    int i = 0 , j = 0;
  
    // Iterate a loop over the
    // range [0, 5]
     for(int i = 0 ; i < 5 ; i ++)
    {
          printf(“i = %d, j = “, i);
  
        // Iterate a loop over the
        // range [0, 5]
        for(int j = 0 ; j < 5 ; J ++){
  
            // Usage of Break statement
             If ( j == 2)
            
                break;
             printf(“%d “, j);
                    }
  
        printf("\n");
    }
  
    return 0;
}

Output

Continue

• This statement is used to bring the control to the beginning of the loop.
• The continue statement skips some lines of code inside the loop and continues with the next iteration.
• It is mainly used in a program for skiiping certain condition.
• This statement does not exit from the loop of the body.
• It is not used to exit from the loop body.
• Continue statement is not used with switch statement.
• It can be used only with while, do while and for loop.
• When the control encounters continue statement,control automatically executes the remaining statements of the loop body.

Syntax

Sample Code

#include <stdio.h>
  
// Driver Code
int main()
{
      Int i = 0 , j = 0 ;
  
    // Iterate the loop over the range[0,5]
    for (int i = 0; i < 5; i++) {
         printf(“i = %d, j = “, i);
        // Iterate the loop over the range[0,5]
        For(int j = 0; j < 5 ; j++){  
         // Usage of Continue Statement
            if (j == 2)
                continue;
              printf("%d ", j);
        }
            printf(“\n”);
            }
  
    return 0;
}

Output

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Syntax

Add(a, b) // a and b are the parameters 

Calling a function in C program

Add.c

#include <stdio.h>  
int add(int a, int b);   
void main()  
{  
  
int sum;  
int a, b;  
printf(" Enter the first and second number \n");  
scanf("%d %d", &a, &b);  
sum = add(a, b); // call add() function  
printf( "The sum of the two number is %d", sum);  
}  
int add(int n1, int n2) // pass n1 and n2 parameter  
{  
int c;  
c = n1 + n2;  
return c;  
}  

Output

Call by value

• When an single or multiple values of an argument are copied into formal parameters of a function, this type of functions is known as Call By Value.
• It does not change the value of the function`s actual parameter.

Call by Value in C programming

Call_Value.c

#include <stdio.h>  
int main()  
{  
int x = 10, y = 20;  
printf (" x = %d, y = %d from main before calling the function", x, y);  
CallValue(x, y);  
printf( "\n x = %d, y = %d from main after calling the function", x, y);  
}  
int CallValue( int x, int y)  
{  
x = x + 5;  
y = y + 5;  
printf (" \nx = %d, y = %d from modular function", x, y);  
}   

Output

Call By Reference

• As name suggests call by reference is a method, where the address of the actual argument is copied into the function call’s formal parameter.
• This type of method is known as Call by Reference.
• If we make some changes in the formal parameters, it shows the effect in the value of the actual parameter.

Call by Reference in C programming

Call_Ref.c

#include <stdio.h>  
int main()  
{  
int x = 10, y = 20;  
printf (" x = %d, y = %d from main before calling the function", x, y);  
CallValue (&x, &y);  
printf( "\n x = %d, y = %d from main after calling the function", x, y);  
}  
int CallRef( int *a, int *b)  
{  
*a = *a + 5;  
*b = *b + 5;  
printf (" \nx = %d, y = %d from modular function", *a, *b);  
}  

Output

]]> https://www.wikitechy.com/interview-questions/c/what-are-called-and-calling-functions/feed/ 0 https://www.wikitechy.com/interview-questions/c/how-many-types-of-data-type-in-c-language/ https://www.wikitechy.com/interview-questions/c/how-many-types-of-data-type-in-c-language/#respond Mon, 03 Oct 2022 12:41:19 +0000 https://www.wikitechy.com/interview-questions/?p=4934 C language supports 3 data types:

• Primary Data Types
• User Defined Data Types
• Secondary Data Types

Primary Data Types

• Integer
• Float
• Char
• Double

User Defined Data Types

• Structure
• Union
• Enum

Secondary Data Types

• Array
• pointers

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Scanf()

• Scanf() is the most commonly used in C langauage.
• They are inbuilt functions in the c program which is in the stdio.h(header file).
• It is an input function in the c program that takes input values from the user.
• It is a function that reads formatted data from stdin(standard input stream), which is keyboard, unless redirected, and then writes the results to arguments.

Printf()

• Printf() is used to display the output.
• They are inbuilt functions in the c program which is in the stdio.h(header file).
• It is a function that prints a string on the screen using a format string that contains mix of several strings.
• It produces a final string to be printed on the screen.
• It is an output function in the c program that prints output values to the console.

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Syntax of While loop

while (testExpression) {
  // the body of the loop 
}

Sample Code

// Print numbers from 1 to 5

#include <stdio.h>
int main() {
  int i = 1;
    
  while (i <= 5) {
    printf("%d\n", i);
    ++i;
  }

  return 0;
}

Output

1
2
3
4
5

Syntax

if (testCondition) {
   // statements
}

Sample Code

#include <stdio.h>
#include <stdbool.h>

int main(void) {
    if(true) {
        printf("Statement is True!\n");
    }

    return 0;
}

Output

Statement is True.

if..else statements

• In an ..else statement, code inside the brackets is executed only if the statement condition evaluates to true.
• If the condition in the if statement evaluates to false, the code inside the else statement is executed.

How does Recursion work

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Rules for switch statement

• Switch expression should be an integer or character data type.
• Case value must be an integer or constant value.
• We can use only case value inside the switch statement.
• Break statement is not mandatory in switch. It is optional.
• If a program does not find a break statement in switch expression, all the cases in the switch will be executed along with the matched case.

Syntax for switch statement

switch(expression){    
case value1:    
//code to be executed;    
break;  //optional  
case value2:    
//code to be executed;    
break;  //optional  
......    
default:     
code to be executed if all cases are not matched;    
}    

Flow chart for switch

Sample Program

    #include<stdio.h>

    int main() {
      int number = 0;
      printf("enter a number:");
      scanf("%d", & number);
      switch (number) {
      case 10:
        printf("number is equals to 10");
        break;
      case 50:
        printf("number is equal to 50");
        break;
      case 100:
        printf("number is equal to 100");
        break;
      default:
        printf("number is not equal to 10, 50 or 100");
      }
      return 0;
    }

Output

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Syntax

static data_type var_name = var_value;

• Here data_type –> Data types like int, char, float etc.
• Var_name -> Name of the variable given by user.
• Value -> Any value to initialize. By default, it is zero.

• A static variable remains in the memory while the program is running.
• Static variables are allocated memory in data segment, not in stack segment.
• Default values of static variables is assigned as 0 if not initialized explicitly.
• In C, static variables can be initialized using constant literals.
• Static global variables and functions are possible in C. The purpose of these is to limit scope of a variable or function to file.
• Static variables cannot be declared inside the structure. The reason is compiler requires the entire structure elements to be placed together.
• Memory allocation for structure members should be contiguous.

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Declaring a pointer

The pointer in c language can be declared using * (asterisk symbol). It is also known as indirection pointer used to dereference a pointer.

int *a; //pointer to int  
char *c;//pointer to char  

Pointer Example:

An example of using pointers to print the address and value is given below.

Pointer to array

int arr[10];  
int *p[10]=&arr; 

Pointer to a function

void show (int);  
void(*p)(int) = &display; 

 Pointer to Structure

struct st {  

   int i;  

    float f;  

}ref;  

struct st *p = &ref;  

Advantages of Pointer

• Pointer reduces the code and improves the performance.
• It is used to retrieving strings, trees, etc., and used with arrays, structures, and functions.
• We can return multiple values from a function using the pointer.
• It makes you able to access any memory location in the computer’s memory.

Usage of pointer

There are many applications of pointers in c language.

Dynamic memory allocation

• In C language, we can dynamically allocate memory using malloc() and calloc() functions where the pointer is used.

Arrays, Functions, and Structures

• Pointers in c language are widely used in arrays, functions, and structures.
• It reduces the code and improves the performance.

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