Everything On Pointers

Pointers in C are variables that hold the memory address of another variable. They enable indirect access to data by "pointing" to the data's location in memory.

Using A Pointer With Stack Memory

To declare a pointer, specify the data type followed by *. Here’s an example where we create an integer x and use a pointer to access its value indirectly

#include <stdio.h>

int main() {
    int x = 10;
    int *ptr;  // Declare a pointer

    ptr = &x;  // Store the address of x in ptr

    printf("Value of x: %d\n", x);
    printf("Value through pointer: %d\n", *ptr);  // Indirectly access x
    return 0;
}

OUTPUT:

Value of x: 10
Value through pointer: 10

Pointers With Heap Memory

You can use malloc to dynamically allocate memory to a pointer. In the following example we use sizeof with an integer to make a pointer with enough memory to store one integer.

Later you can use free to deallocate the memory you assigned in your program. This is important so you avoid memory leaks in your system. A

A memory leak occurs when you allocates memory dynamically but fails to release it after it's no longer needed. This unfreed memory remains reserved by the program, even though it’s no longer in use. Over time, memory leaks can cause a program to consume more and more memory, eventually slowing down the system or causing it to run out of memory, leading to crashes.

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *ptr = (int *)malloc(sizeof(int));  // Allocate memory for an integer
    *ptr = 20;  // Assign value to allocated memory

    printf("Value through pointer: %d\n", *ptr);

    free(ptr);  // Free allocated memory
    return 0;
}

OUTPUT:

Value through pointer: 20

Compiling C With Command Line

You can compile and run your C code from the command line using the gcc tool, which turns your source code into an executable file. Here’s how to do it:

gcc -g -o myProgram main.c

Here’s what each part of the command does:

• gcc is the tool that compiles your code.

• -g is an optional flag that adds debugging information to the complied program. This extra information allows debugging tools like valgrind (see next section)

• -o is an optional flag that lets you specify the name of your executable. In this case, we named it myProgram.

• main.c is your source code file. You can list multiple .c files if your program has more than one.