C++ Programming/Examples

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

// Confusing Scope Program
#include <iostream>
 
using namespace std;
 
int i = 5;           /* The first version of the variable 'i' is now in scope */
 
void p(){
  int i = -1;        /* A ''new'' variable, also called 'i' has come into existence. The 'i' declared above is now out of scope,*/
  i = i + 1;
  cout << i << ' ';  /* so this ''local'' 'i' will print out the value 0.*/
}                    /* The newest variable 'i' is now out of scope. The first variable, also called 'i', is in scope again now.*/
 
 
main(){
  cout << i << ' ';  /* The first variable 'i' is still in scope here so a ''5'' will be output here.*/
  char ch;
  int i = 6;         /* A ''new'' variable, also called 'i' has come into existence. The first variable 'i' is now out of scope again,*/
  i = i + 1;
  p();
  cout << i << endl; /* so this line will print out a ''7''.*/
}                    /* End of program: all variables are, of course, now out of scope.*/

// Program Average
#include <iostream>
 
using namespace std;
 
float a[20];                      /* a is now in scope.*/
int length;                       /* length is now in scope.*/
 
float average(){
  float result = 0.0;             /* result is now in scope.*/
 
  for(int i = 0; i < length; i++){ /* i is now in scope.*/
   result += a[i];
  }                               /* i is now out of scope.*/
 
  return result/length;
}                                 /* result is now out of scope.*/
 
int main(){
 length = 0;
 while(cin >> a[length++]){
 };
 length--;
 float av = average();            /* av is now in scope.*/
 cout << av << endl;
}                                 /* All variables now out of scope.*/

// Program Average rewritten using a class
#include <iostream>
 
using namespace std;
 
class StatisticsPackage{
private:
  float aa[20];                     /* aa scope start*/
  int length;                       /* length scope start*/
public:                           
  float average(){
    float result = 0.0;             /* result scope start*/
 
    for(int i = 0; i < length; ++i) /* i scope start*/
      result += aa[i];
 
  return result/length;
  }                                 /* result and i scope end*/
 
  void get_data(){
    length = 0;
    while(cin >> aa[length++]);
    --length;
  }
};                                  /* aa and length scope end*/
 
main(){
  StatisticsPackage sp;             /* aa and length lifetimes start */
  sp.get_data();
  float av = sp.average();          /* av scope start*/
  cout << av << endl;
}                                   /* av scope end*/

// Complicated Scope Program
#include <iostream>
 
using namespace std;  /* outermost level of scope starts here */
 
int i;
 
main(){               /* next level of scope starts here */
  int i;
  i = 5;
 
  {                   /* next level of scope starts here */
    int j,i;
    j = 1;
    i = 0;
 
    {                 /* innermost level of scope of this program starts here */
      int k, i;
      i = -1;
      j = 6;
      k = 2;
    }                 /* innermost level of scope of this program ends here */
 
    cout << j << ' ';
  }                   /* next level of scope ends here */
 
  cout << i << endl;
}                     /* next and outermost levels of scope end here */

// Complicated Scope Program, variation 1
#include <iostream>  
 
using namespace std;  /* outermost level of scope starts here */
 
int i;
 
main(){               /* next level of scope starts here */
  int i;
  i = 5;
 
  while(i != 5) {     /* next level of scope starts here */
    int j,i;
    j = 1;
    i = 0;
    switch (i) {      /* next level of scope starts here */
      int i;
 
      case 1:
        if (i != 4) { /* innermost level of scope of this program starts here */
          int k, i;
          i = -1;
          j = 6;
          k = 2;
        }             /* innermost level of scope of this program ends here */
        break;
 
      case 2: 
        j = 5;
        break;
    }                 /* next level of scope ends here */
 
    cout << j << ' ';
  }                   /* next level of scope ends here */
 
  cout << i << endl;
}                     /* next and outermost levels of scope end here */

// Complicated Scope Program, variation 2
#include <iostream>
 
using namespace std; /* outermost level of scope starts here */
 
int i;
 
main(){              /* next level of scope starts here */
  int i;
  i = 5;
 
  for(               /* next level of scope starts here */
      int i = 1;
      i<10 && cout << i << ' ';
      ++i )  
  {                  /* next level of scope starts here */
    int i = -1;
    cout << i << ' ';
  }                  /* two levels of scope end here*/
 
  cout << i << endl;
}                    /* next and outermost levels of scope end here */

// Namespaces Program, an example to illustrate the use of namespaces
#include <iostream>
 
namespace first {
  int first1;
  int x;
}
 
namespace second {
  int second1;
  int x;
}
 
namespace first {
  int first2;
}
 
main(){
  //first1 = 1;
  first::first1 = 1;
  using namespace first;
  first1 = 1;
  x = 1;
  second::x = 1;
  using namespace second;
 
  //x = 1;
  first::x = 1;
  second::x = 1;
  first2 = 1;
 
  //cout << 'X';
  std::cout << 'X';
  using namespace std;
  cout << 'X';
}

// This program adds two numbers and prints their sum.
#include <iostream.h>
 
int main()
{
  int a = 123;
  int b (456);
  int sum;
 
  sum = a + b;
 
  std::cout << "The sum of " << a << " and " << b << " is " << sum << "\n";
 
  return 0;
}

// This program adds two numbers and prints their sum, variation 1
#include <iostream>
#include <ostream>
 
using namespace std;
 
int main()
{
  int a = 123, b (456), sum = a + b;
 
  cout << "The sum of " << a << " and " << b << " is " << sum << endl;
 
  return 0;
}

// very simple C++ program using a class.
 
#include <iostream>
 
class myClass
{
public:
 myClass(int);
 
private:
 int i;
};
 
myClass::myClass(int x) : i(x) {}
 
int main()
{
  myClass my_class(5);
 
  // dynamic
  myClass* my_class_ptr = new myClass(5);
  delete my_class_ptr;
 
  return 0;
}

// This program justs displays a string and exits
#include <iostream>
 
int main()
{
  std::cout << "Hello World!";
  std::cout << std::endl;
 
return 0;
}

// This program justs displays a string and exits, variation 1
#include <iostream>
 
int main() { std::cout<<"Hello World!"; std::cout<<std::endl; return 0; }

// This program justs displays a string and exits, variation 2
#include <iostream>
 
int main() {
  std::cout << "Hello World!";
  std::cout << std::endl;
 
return 0;
}