C++ Programming/Scope/Examples

Scope

Confusing Scope Program

// 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.*/

int 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''.*/
  return 0;
}                    /* End of program: all variables are, of course, now out of scope.*/

Average Program

// Program Average
#include <iostream>

using namespace std;

float a[10];                      /* 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;
  cout << "enter a number for each of the next 10 lines" << endl;

  while( length != 10 )
    { cin >> a[length++]; }

  float av = average();            /* av is now in scope.*/
  cout << endl << "average: " << av << endl;

  return 0;
}                                 /* 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*/

int main(){
  StatisticsPackage sp;             /* aa and length lifetimes start */
  sp.get_data();
  float av = sp.average();          /* av scope start*/
  cout << av << endl;
  return 0;
}                                   /* av scope end*/

Complicated Scope Program

// Complicated Scope Program
#include <iostream>
  
using namespace std;  /* outermost level of scope starts here */

int i;

int 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;
  return 0;
}                     /* 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;

int 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;
  return 0;
}                     /* 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;

int 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;
  return 0;
}                    /* next and outermost levels of scope end here */

Namespaces Program

// 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;
}

int 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';
  return 0;
}