Control Structures

Control Structures

Conditional structure: if and else

if (condition) statement:

if (x == 100)
  cout << "x is 100";

if we want more than a single statement to be executed in case that the condition is true we can specify a block using braces {}:

if (x == 100){
  cout << "x is ";
  cout << x;
}

if (condition) statement1 else statement2

For example1:

if (x == 100)
  cout << "x is 100";
else
  cout << "x is not 100"

For example2:

if (x > 0)
  cout << "x is positive";
else if (x < 0)
  cout << "x is negative";
else
  cout << "x is 0";

The while loop:

while (expression) statement

while.cpp

// custom countdown using while

#include <iostream>
using namespace std;

int main(void){

  int n;

  cout << "Enter the starting number > ";
  cin >> n;

  while(n > 0){
    cout << n << ", ";
    --n;
  }

  cout << "FIRE!\n";
  
  return 0;
}

while.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./while
Enter the starting number > 10
10, 9, 8, 7, 6, 5, 4, 3, 2, 1, FIRE!

dowhile.cpp

// number echoer

#include <iostream>
using namespace std;

int main(void){

  unsigned long n;
  do{
    cout << "Enter number (0 to end): ";
    cin >> n;
    cout << "You entered: " << n << "\n";
  }while(n != 0);
  
  return 0;
}

dowhile.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./dowhile
Enter number (0 to end): 10
You entered: 10
Enter number (0 to end): 20
You entered: 20
Enter number (0 to end): 30
You entered: 30
Enter number (0 to end): 0
You entered: 0

The for loop

Its format is:

for (initialization; condition; increase) statement;

forloop.cpp

// countdown using a for loop

#include <iostream>
using namespace std;

int main(void){

  for(int n = 10; n > 0; n--){
    cout << n << ", ";
  }
  cout << "FIRE!\n";
  
  return 0;
}

forloop.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./forloop
10, 9, 8, 7, 6, 5, 4, 3, 2, 1, FIRE!

The break statement

break.cpp

// break loop example

#include <iostream>
using namespace std;

int main(void){

  int n;

  for(n = 10; n > 0; n--){
    cout << n << ", ";
    if(n == 3){
      cout << "countdown aborted!\n";
      break;
    }
  }
  return 0;
}

break.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./break
10, 9, 8, 7, 6, 5, 4, 3, countdown aborted!

The continue statement

continue.cpp

// continue loop example

#include <iostream>
using namespace std;

int main(void){

  for(int n = 10; n > 0; n--){
    if(n == 5) continue;
    cout << n << ", ";
  }

  cout << "FIRE!\n";

  return 0;
}

continue.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./continue
10, 9, 8, 7, 6, 4, 3, 2, 1, FIRE!

The goto statement

// goto loop example

#include <iostream>
using namespace std;

int main(void){

  int n = 10;
  
 loop:
  cout << n << ", ";
  n--;
  if (n > 0) goto loop;

  cout << "FIRE!\n";

  return 0;
}

goto.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./goto
10, 9, 8, 7, 6, 5, 4, 3, 2, 1, FIRE!

The exit function:

void exit(int exitcode);

The selective structure:switch

Functions (I)

func.cpp

// function example

#include <iostream>
using namespace std;

int addition(int a, int b){
  int r;
  r = a + b;
  return r;
}

int main(void){

  int z;

  z = addition(45, 55);
  cout << "The result is " << z << endl;

  return 0;
}

func.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./func
The result is 100

func2.cpp

// function2 example

#include <iostream>
using namespace std;

int subtraction(int a, int b){
  int r;
  r = a - b;
  return r;
}

int main(void){

  int x = 4;
  int y = 3;
  int z;

  z = subtraction(7, 2);

  cout << "The first result is " << z << '\n';

  cout << "The second result is " << subtraction(7, 2) << '\n';

  cout << "The third result is " << subtraction(x, y) << '\n';

  z = 4 + subtraction(x, y);

  cout << "The fourth result is " << z << '\n';

  return 0;
}

func2.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./func2
The first result is 5
The second result is 5
The third result is 1
The fourth result is 5

voidfunc.cpp

// void function example

#include <iostream>
using namespace std;

void printmessage(){
  cout << "I'm a function!\n";
}

int main(void){

  printmessage();

  return 0;
}

voidfunc.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./voidfunc
I'm a function!

Functions (II)

Arguments passed by value and by reference

referfunc.cpp

// passing parameters by reference

#include <iostream>
using namespace std;

void duplicate(int& a, int& b, int& c){
  a *= 2;
  b *= 2;
  c *= 2;
}

int main(void){

  int x = 1;
  int y = 3;
  int z = 5;

  duplicate(x, y, z);

  cout << "x = " << x << endl;
  cout << "y = " << y << endl;
  cout << "z = " << z << endl;

  return 0;
}

referfunc.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./referfunc.cpp
x = 2
y = 6
z = 10

referfunc1.cpp

// more than one returning value

#include <iostream>
using namespace std;

void prevnext(int x, int& prev, int& next){
  prev = x - 1;
  next = x + 1;
}

int main(void){

  int x = 100;
  int y;
  int z;

  prevnext(x, y, z);

  cout << "Previous = " << y << endl;
  cout << "x = " << x << endl;
  cout << "Next = " << z << endl;

  return 0;
}

referfunc1.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./referfunc1
Previous = 99
x = 100
Next = 101

Default values in parameters

deffunc.cpp

// default values in functions

#include <iostream>
using namespace std;

int divide(int a, int b = 2){
  int r;
  r = a / b;
  return r;
}

int main(void){

  cout << "divide(12) = " << divide(12) << endl;

  cout << "divide(20, 4) = " << divide(20, 4) << endl;

  return 0;
}

deffunc.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./deffunc
divide(12) = 6
divide(20, 4) = 5

Overloaded functions

overfunc.cpp

// overloaded function

#include <iostream>
using namespace std;

int operate(int a, int b){
  return a * b;
}

float operate(float a, float b){
  return a * b;
}


int main(void){

  int x = 5, y = 2;
  float m = 5.2, n = 2.2;

  cout << "int operate(int a, int b) = " << operate(x, y) << endl;
  
  cout << "float operate(float a, float b) = " << operate(m, n) << endl;

  return 0;
}

overfunc.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./overfunc
int operate(int a, int b) = 10
float operate(float a, float b) = 11.44

Recursivity

factorial.cpp

// factoiral calculator

#include <iostream>
using namespace std;

long fac(long a){
  if(a > 1)
    return a * fac(a-1);
  else
    return 1;
}

int main(void){

  long num;

  cout << "Please type a number: ";
  
  cin >> num;
    
  cout << num << "! = " << fac(num) << endl;

  return 0;
}

factorial.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./factorial
Please type a number: 5
5! = 120
[cactus:~/code_c++/cpp_tuts]% ./factorial
Please type a number: 10
10! = 3628800
[cactus:~/code_c++/cpp_tuts]% ./factorial
Please type a number: 25
25! = 7034535277573963776

Declaring functions

declare.cpp

// declaring functions prototypes

#include <iostream>
using namespace std;

void odd(int a);
void even(int a);

int main(void){

  int i;

  do{
    cout << "Type a number (0 to exit): ";
    cin >> i;
    odd(i);

  }while(i != 0);
  
  return 0;
}

void odd(int a){
  if( (a%2) != 0)
    cout << "Number is odd.\n";
  else
    even(a);
}

void even(int a){
  if( (a%2) == 0)
    cout << "Number is even.\n";
  else
    odd(a);
}

declare.cpp の実行結果は:

[cactus:~/code_c++/cpp_tuts]% ./declare
Type a number (0 to exit): 20
Number is even.
Type a number (0 to exit): 21
Number is odd.
Type a number (0 to exit): 15
Number is odd.
Type a number (0 to exit): 57
Number is odd.
Type a number (0 to exit): 0
Number is even.