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Review

Ch 1:

Arrays

  • Arrays must have the same data types inside.
  • Used to implement other data structures.
  • Always contiguous in memory.
  • Array can not change size in most languages.
### Initializing Arrays 
int A[5]; // array will be initialized by garbage
int B[5] = {1, 2, 3, 4, 500};
int C[5] = {1, 2}; // Others will be initialized by 0
int D[] = {1, 2, 3, 4, 5, 9}; //Array of 6 is created
### Accessing Arrays 
cout << A[1] // Using index
  << 1[A]    // Using index outside
  << *(A+1)  // Using pointer
  << endl;
for (int i = 0; i < A.size(); i++) { // Accessing the whole array
  cout << A[i] << endl;  
}
### Array Memory Location 
// This code prints the memory locations of each element of the array.
// Shows contiguous
int A[5] = {2, 4, 7, 2, 9};
for (int i = 0; i < A.size(); i++) {
  cout << &A[i] << endl; 
  // The & means return memory location instead of value at location
}

Pointers: indirect addressing (think of a library and books)

  • Value stored in variable (book)
  • Variable stored in location (shelf)
  • Address (floor number + shelf number + location number) <- used to access memory location of variable
  • Name (name of bookshelf ["new books", "math"]) <- not all locations have a name.
  • Pointer (an index card for a book that tells you where to find book)
    • Pointer is also a variable so it has its own (value, location, address, name)

Pointer = variable whose value is the address of another variable.

  • Pointer (address type is common in C/C++)
  • Operations on pointers:
    • & = Referencing: Obtain address of variable from its name
    • * = Dereferencing: Create a variable name for a given address
### Referencing 
#include <iostream>

using namespace std;
int main() {
  int var1;
  char var2[10];

  cout << "var1 address: " << &var1 << endl;
  cout << "var2 address: " << &var2 << endl;

  return 0;
}
Output:
  var1 address: 0xbfebd5c0
  var2 address: 0xbfebd5c6
### Dereferencing 
int x = 3;
int *y;
y = &x;
// *y is an l-value (left  side)
// &x is a  r-value (right side)
int x, *y;
// Initial states
  // Address of x: 2000
  // value of x: 500
  // value of y: 8000
y = &x;     // value of y: 2000
*y = 100;   // value of x: 100
y = y + 10; // value of y: 2040 (2000 + 10 cells * 4 bytes/cell)
*y = 100;   // Points to an unknown location, **issue**!

Ch 2: