using Directive

• Similar to Java's import
  • Uses a namespace, which is somewhat similar to a Java package
  • Allows the programmer to not have to type the full namespace name each time

// C++
#include <iostream>
using namespace std;
int main() {
    cout << "Hello World!" 
         << endl;
    return 0;
}

// C++
#include <iostream>
int main() {
    std::cout << "Hello World!" 
              << std::endl;
    return 0;
}

Error comparison

g++:
clang++:

Declaring mutually
recursive functions

Source code: evenodd.cpp (src)

bool even (int x);

bool odd (int x) {
    if ( x == 0 )
        return false;
    else
        return even (x-1);
}
	  

bool even (int x) {
    if ( x == 0 )
        return true;
    else
      return odd (x-1);
}
	  

Pointer Variables

Source code: pointers.cpp (src)

int x = 1;
int y = 5;
int * x_pointer = &x;
cout << x_pointer;
cout << *x_pointer;

x_pointer = &x

*x_pointer = 2

x_pointer = &y

*x_pointer = 3

Pointer Pitfalls: Uninitialized Pointers

• Cause runtime errors

  int n = 30;
  int * p;
  *p = n;    //ERROR!!!
  

  • p does not have a valid memory address!
  • A common initializer value used by programmers is NULL

    int *p=NULL; // better code, then add code to check 
                 // for NULL value
    

swap()

Source code: swap.cpp (src)

void swap(int * x, int * y) {
    int temp = *x;
    *x = *y;
    *y = temp;
}