What is ## operator in C?

C Programming Language > C Pre-processor > Introduction about Pre-processor

Long Question

776

Answer:

## is a pre-processor macro in C. It is used to concatenate 2 tokens into one token.


#include<stdio.h>

#define concatination(a,b) a ## b

int main ()
{
  int ab = 1000;
 printf("The concatenated value is:%d \n",concatination(a,b));
 return 0;
}

Output:

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664. What is pragma in C? Or how will you execute functions before and after main function in C program?

Answer:
#pragma is a pre-processor macro in C. It is used to call a function before and after main function in a C program.

Parameters:

destination: A pointer to the destination character array where the string will be copied.

source: A pointer to the source character array, which contains the string to be copied.

Return Value:

The strcpy() function returns a pointer to the destination character array (destination).

Example Usage:

In the above example, the strcpy() function is used to copy the contents of the source array to the destination array. After the strcpy() function is called, the destination array will contain the same string as the source array, "Hello, World!". The resulting string is then printed using printf().

It's important to note that when using strcpy(), you need to ensure that the destination array is large enough to accommodate the copied string to avoid buffer overflow and memory corruption.

# Tutorial: Introduction to String
Question: String in C Language Short

671. Can array subscripts have negative value in C?

Answer:
No. Array subscripts should not have a negative value. Always, it should be positive.

No, array subscripts cannot have negative values in C. Array subscripts are used to access individual elements of an array by specifying their position or index. In C, array indexing starts from zero, so the first element of an array has an index of 0, the second element has an index of 1, and so on.

Attempting to use a negative value as an array subscript would result in undefined behavior. It can lead to memory access errors, data corruption, or program crashes. It is important to ensure that array subscripts are within the valid range of the array size to access elements correctly and avoid unintended consequences.

# Tutorial: Single Dimensional Array
Question: Array in C Language Short

672. What is the difference between array and string in C?

Answer:

Array can hold any of the data types. But, string can hold only char data type.

Array size must be a constant value. So, array size can’t be changed once declared. But, string size can be modified using char pointer.

Array is not ended with null character by default. But, string is ended with null (‘\0’) character by default.

Here's a comparison between arrays and strings in C:

Aspect Array String

Definition A collection of elements of the same data type. A sequence of characters terminated by a null character ('\0').

Data Type Can store elements of any data type (e.g., int, char, etc.). Specifically stores characters (char type) or an array of characters.

Initialization Can be initialized with default values or specific elements. Can be initialized using string literals or an array of characters.

Termination No specific termination character. Terminated by a null character ('\0') to indicate the end of the string.

Size Size is determined by the number of elements in the array. Size is determined by the length of the string, excluding the null terminator.

Access Elements accessed using array indexing. Individual characters can be accessed using array indexing or string manipulation functions.

Modification Elements can be modified individually. Characters within a string can be modified, but the length of the string cannot be changed directly.

Functions Array-specific functions can be used for manipulation. String-specific functions from the C standard library (<string.h>) can be used for manipulation.

In summary, an array in C is a collection of elements of the same data type, while a string is a sequence of characters terminated by a null character. Arrays can store elements of any data type, whereas strings specifically store characters or arrays of characters. Strings have a special termination character ('\0') to indicate the end of the string. Arrays are accessed and modified using array indexing, while strings can be manipulated using string-specific functions from the C standard library.

# Tutorial: Introduction to String
Question: String in C Language Short

673. What is null pointer in C?

Answer:
Null pointer is a pointer which is pointing to nothing. Null pointer points to empty location in memory. Value of null pointer is 0. We can make a pointer to point to null as below.

int *p = NULL;
char *p = NULL;

In C, a null pointer is a special value that represents the absence of a valid memory address. It is commonly denoted by the macro NULL, which expands to an implementation-defined null pointer constant.

A null pointer does not point to any valid memory location. It is used to indicate that a pointer variable does not currently point to an object or has not been assigned a valid memory address yet.

Null pointers are often used in conditional statements to check if a pointer is valid or uninitialized before dereferencing it. Attempting to dereference a null pointer can result in undefined behavior, such as program crashes or accessing invalid memory.

Here's an example illustrating the use of null pointers:

In the above example, a pointer variable ptr is initialized with a null pointer by assigning the NULL macro. The code then checks if ptr is equal to NULL using an if statement. Since ptr is a null pointer, the message "The pointer is currently null." is printed.

# Tutorial: NULL pointer
Question: Pointer in C Language Short

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Aspect	Array	String
Definition	A collection of elements of the same data type.	A sequence of characters terminated by a null character (`'\0'`).
Data Type	Can store elements of any data type (e.g., int, char, etc.).	Specifically stores characters (`char` type) or an array of characters.
Initialization	Can be initialized with default values or specific elements.	Can be initialized using string literals or an array of characters.
Termination	No specific termination character.	Terminated by a null character (`'\0'`) to indicate the end of the string.
Size	Size is determined by the number of elements in the array.	Size is determined by the length of the string, excluding the null terminator.
Access	Elements accessed using array indexing.	Individual characters can be accessed using array indexing or string manipulation functions.
Modification	Elements can be modified individually.	Characters within a string can be modified, but the length of the string cannot be changed directly.
Functions	Array-specific functions can be used for manipulation.	String-specific functions from the C standard library (`<string.h>`) can be used for manipulation.

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