float square(float x)
{
  return x * x;
}

 #include <iostream.h> // allows use of >> and << for I/O
int main() //  int is the  exit status for main
{
  cout << "Hello Everyone!\n";
  return 0; // 0 means program terminated  ok
}

double average( double x, double y );
double toFarenheight( double centegradeTemp );
double toCentegrade( double farenheightTemp );

double average( double x, double y )
{
  return ( x + y ) / 2.0;
}
double toFarenheight( double centegradeTemp )
{
  return 9.0 * centegradeTemp / 5.0 + 32.0;
}
double toCentegrade( double farenheightTemp )
{
  return 5.0 * ( farenheightTemp - 32.0 ) / 9.0;
}

int main()
{
  double x = 10.5;
  double y = 32.6;
  double z = average( x, y );
  double centegradeTemp = 22.3;
  double farenheightTemp = toFarenheight( centegradeTemp );
  cout << toFarenheight( centegradeTemp + 2.0 ) << endl;
  cout << average( toFarenheight( 29.7 ),
          toFarenheight( centegradeTemp ) );
  return 0;
}

double average( double x, double y )
{
  return ( x + y ) / 2.0;
}

double x = 5.0;
double z = average( 1.0, 2.0*x );

double toCentegrade( double farenheightTemp = 32.0 )
{
  return 5.0 * ( farenheightTemp - 32.0 ) / 9.0;
}

double t = toCentegrade(); // gives the Centegrade for 32.0
cout << toCentegrade( 6.0 ); // overrides the default with 6.0

float square(float x)
{
  float result = x * x;
  cout << "Hello there!\n";
  return result;
  cout << "Hello there again!\n";
}
int main()
{
  cout << square( 2.0 );
  cout << square( square( 2.0 ) );
  return 0;
}

0
1
-1
-1234567
11 // decimal 11
011 // octal 9
0x11 // hex 17

1.0
-3.000001e-10
30.01E40

0 to 255

'\0' null character 0
'\n' newline (or linefeed) 10
'\r' return 13
'\t' tab 9
' ' space 32
'0' 48
'A' 65
'a' 97

char *s = "Hello";

char *t = "Hello world!";
cout << "This is another character string.\n";
cout << t << endl; // prints: Hello World!

int numberOfStudentsInECE10 = 160;
int automobileVelocity = 0;

numberOfStudentsInECE10 = 175; // added a few students
automobileVelocity += 20; // accelerated the auto

const double PI = 3.1415926536;
const char newline = '\n';
const int roomCapacity = 250;

PI = 3.0; // compiler will give a warning message

return 3.14159*r*r;
return PI*r*r;

int main()
{
  const double PI = 3.14159;
  double i = 2.0 * PI;
  cout << i << endl;
  i = i / 2.0;
  square( 2.0 ); // be careful of this mistake
  cout << i << endl;
  return 0;
}

int f( int a, int j ) // a and j are now in scope
{
  int i = 10; // i is now in scope
  {
    int j = i; // new j is now in scope and hides parameter j
    int i = 30; // this new i is in scope and hides outer i
    cout << i * j << endl; // refers to inner i and j
  } // inner j and i are now out of scope
  cout << i << endl;
  return a + j + i; // refers to the parameters and outer i
} // a, j, i are now out of scope
int main()
{
  int a = 10;  // a is in scope
  int i = 20;  // i is in scope
  cout << f( i, a ); // calls f with actual values 20 and 10
  return 0;
} // a and i are now out of scope

void increment(int & x)
{
  x = x + 1;
}
int main()
{
  int z = 10;
  increment(z);
  increment(z);
  cout << z;
  return 0;
}

int main()
{
  cout << "Hello";
  cout << 10 * 10;
  cout << 'A';
  cout << 3.14159;
  ...
}

int main()
{
  int i;
  float f;
  char c;
  cin >> i;  // reads a string of digits as an integer
  cin >> f; // reads a string of digits, decimal as a real number
  cin >> c; // reads a single character
  ...
}

 #include <iostream.h>
int main()
{
  int i = 40;
  cout << "I is " << i << endl;
  return 0;
}