CNotes6.md

Pointers

The topic of pointers in C is one that many beginners find challenging. In order to understand pointers it is first imperative that you have a strong grasp of the variables that we have been programming with so far.

A pointer is a special type of variable (it's actually a constant?) whose value is the memory address of another variable. (make this sound less confusing)

A pointer variable is declared by prefacing its name with an asterisk:

 int main(){
     int *pointer;
     
     return 0;
 }

Convention

In many cases the accepted convention is to start a pointer variable with the letter p, for example:

 int main(){
    //create an integer variable
     int age;

     //create a pointer variable
     int *pAge;
    
     return 0;
 }

Where are variables stored in memory?

To acces memory locations in C use a pointer thingy:

%p

We can echo a memory address to the console using something like the following snippet:

    int i = 42;

    printf("%p ", i);

    return 0;

Some notes on Hex.

Creating Pointers:

Take for example: int myInt = 42, this can store any numeric value between x and y. It has a memory address and we can create int * pMyInt = &myInt

Dereference Pointer

If you want to retrieve the value that a pointer points to (as opposed to the address that it points to) then you use the unary operator, *, which is used to dereference the pointer.

 int i = 42;
 int *prt = &i;

 int main(){
     printf("The address of int i is: %p \n", prt);
     printf("The value stored  at i is: %d \n", *prt);
     
     return 0;
 }

Arrays and Pointers

create and array of vars loop through the array and print it's contents, and memory pointer.

int luckyNums[6] = [4,8,15,16,23,42];

printf(" Element \t Address \t Value")
for (i=0; i<6; i++){
    printf(" luckyNums[%d] \t %p \t %d", i, &luckyNums[i], luckyNums[i]);
}

//array names are just pointers to the first element of that array.
printf("\n luckyNums %p", luckyNums);

Strings and Pointers

Test it Out

 int main(){
    j = 1;
    k = 2;
    ptr = &k;
    printf("\n");
    printf("j has the value %d and is stored at %p\n", j, (void *)&j);
    printf("k has the value %d and is stored at %p\n", k, (void *)&k);
    printf("ptr has the value %p and is stored at %p\n", ptr, (void *)&ptr);
    printf("The value of the integer pointed to by ptr is %d\n", *ptr);
     
     return 0;
 }