Functions, Arrays, Pointers, and the interaction of Pointers & Arrays in C

 

Here’s a breakdown of Functions, Arrays, Pointers, and the interaction of Pointers & Arrays in C:

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1. Functions in C

• A function is a reusable block of code that performs a specific task. Functions help organize code and enable modular programming.
• Syntax:

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return_type function_name(parameter_list) {

    // code

    return value; // (if return_type is not void)

}

• Example:

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int add(int a, int b) {

    return a + b;

}

• Function Types:
• Standard Library Functions: Functions like printf() and scanf().
• User-defined Functions: Functions defined by the programmer, like add() in the example above.
• Function Declaration and Definition:
• Declaration (prototype) informs the compiler about a function.
• Definition contains the actual body of the function.

2. Arrays in C

• An array is a collection of elements of the same data type stored at contiguous memory locations.
• Arrays allow storing multiple values of a single type in a single variable.
• Syntax:

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data_type array_name[array_size];

• Example:

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int numbers[5] = {1, 2, 3, 4, 5};

• Accessing Elements:
• Elements are accessed using an index, starting from 0.

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int first_element = numbers[0]; // Accesses the first element (1)

• Multidimensional Arrays:
• Example of a 2D array:

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int matrix[3][3] = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} };

3. Pointers in C

• A pointer is a variable that stores the memory address of another variable.
• Syntax:

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data_type *pointer_name;

• Example:

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int x = 10;

int *ptr = &x; // ptr holds the address of x

• Pointer Operations:
• Dereferencing: Accessing the value at the pointer’s address using *.

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int value = *ptr; // value is 10

• Pointer Arithmetic: You can move the pointer to access adjacent memory locations.

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ptr++; // Moves the pointer to the next memory location for the same data type

4. Pointers and Arrays in C

• In C, arrays and pointers are closely related. The name of an array acts as a pointer to the first element.
• Accessing Array Elements with Pointers:

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int arr[5] = {10, 20, 30, 40, 50};

int *ptr = arr; // ptr points to the first element of arr

 

printf("%d\n", *ptr);       // Outputs 10

printf("%d\n", *(ptr + 1)); // Outputs 20

• Pointer to an Array:
• You can use a pointer to iterate over an array:

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for (int i = 0; i < 5; i++) {

    printf("%d ", *(arr + i)); // Outputs each element in arr

}

• Array of Pointers:
• An array where each element is a pointer. This is useful for arrays of strings.

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char *names[] = {"Alice", "Bob", "Charlie"};

printf("%s\n", names[0]); // Outputs "Alice"

• Pointer to a Function:
• You can use pointers to store function addresses, enabling functions to be passed as arguments.

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int (*func_ptr)(int, int) = &add; // func_ptr points to the add function

int result = func_ptr(5, 3); // Calls the add function using the pointer

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These fundamentals are essential in C, as pointers allow efficient memory management and manipulation, and arrays provide a structured way to handle collections of data.