void main() {
// Each of these variables will have a place of 4 bytes in the memory
// And each of those areas of memory are going to have an address, which
// we are going to use to set data. We can actually return set address.
int rand1 = 12, rand2 = 15;
// %p - means percent
// We will get hex code for the location in the memory
printf("rand1 = %p : rand2 = %p\n\n", &rand1, &rand2);
// The decimal verison of the previous row of code
printf("rand1 = %d : rand2 = %d\n\n", &rand1, &rand2);
printf("Size of int %d\n\n", sizeof(rand1));
// After this trick you will see that very often values of variables
// are stored in the memory not close to each other. They are stored
// in the different places.
// If we will need to access the data and the location of some date
// in the memory, we may use pointers. We are gonna to use the same
// data type for our pointer. And very often pointer are going to
// have a p in front of them.
// & - getting the addres in the memory
// p - means that is the pointer
int * pRand1 = &rand1;
printf("Pointer = %p\n\n", pRand1);
printf("Pointer = %d\n\n", pRand1);
// But if we want to get the data that is stored in the exact location
// of memory, using pointers, we gonna use an asterisk - *.
// It is called derefferencing the pointer. It means to use the pointer
// to access the value.
printf("Value %d\n\n", *pRand1);
int primeNumbers[] = {2,3,5,7};
// Printing the value by index
printf("First index %d\n\n", primeNumbers[0]);
// But another way to print it - is using the asterisk
// The asterisk is going to print out the first index value
printf("First index %d\n\n", *primeNumbers);
// But how we are going to get the other index?
// What we should do to get 3 value from the array?
printf("First index %d\n\n", primeNumbers[1]);
// Here we are gonna use Pointer Arithmetic
// In essence we are going to do is adding 1 to the address
printf("First index %d\n\n", (*primeNumbers + 1));
// How we work with arrays of strings?
// We are going to create an array of strings by
// creating an arrays of pointers
char * students[4] = {"Sally", "Mark", "Paul", "Sue"};
// Now we want to retrieve them
for(int i = 0; i < 4; i++){
// Every name is a string, so we use %s
// and %d - we want to know address
// This will give us all the names with their memory locations
printf("%s : %d\n\n", students[i], &students[i]);
}
// How to use this with functions?
int rand1 = 0, rand2 = 0;
generateTwoRandomNums(rand1, rand2);
// the generateTwoRandomNums will not change the values
// but here the values will be the same: 0 and 0
printf("rand1 = %d\n\n", rand1);
printf("rand2 = %d\n\n", rand2);
// So what can we do?
// We have to use pointers.
printf("Main before function call\n\n");
printf("rand1 = %d\n\n", rand1);
printf("rand2 = %d\n\n", rand2);
// But in this situation we are going to pass an address
// We just add '&' to the function arguments
pointerRandomNumbers(rand1, rand2);
printf("Main after function call\n\n");
// now this new function will change the values
printf("rand1 = %d\n\n", rand1);
printf("rand2 = %d\n\n", rand2);
// We are going to create random message
char randomMessage[] = "Edit my function";
printf("Old Message: %s\n\n", randomMessage);
editMessageSent(randomMessage, sizeof(randomMessage));
printf("New Message: %s\n\n", randomMessage);
}
int main(){
// When you compile and run your program you are provided
// with a piece of memory in ram to store data like
// variables.
int rand1 = 12, rand2 = 15;
// Each time you create an int 4 bytes of data are saved
// and that part of memory has an address you can use
// to locate the data.
// You can return that address by placing a & before
// the variable name in c.
printf("rand1 = %p : rand2 = %p\n\n", &rand1, &rand2);
// Sometimes these variables are stored next to each other
// and at other times that isn't true
printf("Size of int %d\n\n", sizeof(int));
// To assign the address to another variable proceed it with
// an asterisk *
int * pRand1 = &rand1;
// If we use %p we get the hexadecimal version of the address
printf("Pointer %p\n\n", pRand1);
// If we use %d we get the decimal version of the address
printf("Value %d\n\n", pRand1);
// We have to use the * to get the value stored there
// This is known as dereferencing the pointer
// Dereferencing means to use the pointer to access the variable
printf("Value %d\n\n", *pRand1);
int randx = 0, randy = 0;
printf("Main before function call\n\n");
printf("randx = %d\n\n", randx);
printf("randy = %d\n\n", randy);
pointerRandomNumbers(&randx, &randy);
printf("Main After function call\n\n");
printf("randx = %d\n\n", randx);
printf("randy = %d\n\n", randh);
// ARRAYS AND POINTERS
// An array name is pretty much a pointer
int primeNumbers[] = {2,3,5,7};
// We can print the values by index
printf("First index : %d\n\n",
primeNumbers[0]);
// You can print the first value also with *
printf("First index with * : %d\n\n",
*primeNumbers);
// You can use pointer arithmetic to access the other values
// with *
// This is in essence adding 1 to the address and since
// it contains ints it jumps 4 bytes forward
// Yes you can use it to get other data stored in memory
printf("Second index with * : %d\n\n",
*(primeNumbers + 1));
// ARRAYS OF STRINGS
// To create an array of strings, you have to create an
// array of pointers
char * students[4] = {"Sally", "Mark", "Paul", "Sue"};
// You can retrieve them now like any other data in an array
for(int i = 0; i < 4; i++){
printf("%s : %d\n\n", students[i], &students[i]);
}
char randommessage[] = "Edit my message";
printf("Old Message: %s \n\n", randomMessage);
editMessageSent(randomMessage, sizeof(randomMessage));
printf("New Message: %s \n\n", randomMessage);
return (0);
}
