Lesson of 7 July 2009

Some simple C programs

A minimal program

File example1.cc

/*
  A multiline comment.
 */
 
// a single line comment


/*
   A simple program that write "ciao mamma" to the console
 */

#include "myinclude.h"
#include <stdio.h>

int // the return type of the main function
main() {  // main is the entry point of the executable
  printf("ciao mamma\n") ; // \n is the new line character
  return 0 ; // exit from the program, all thing go well
}

Example of types and keyrowds of C

File example2.cc

/*
   Introduction to the type of C
 */

#include <stdio.h>

int // the return type of the main function
main() {  // main is the entry point of the executable
  int       a, b, c ;    // declare the variable a, b and c as of integer type (normally 4 byte)
  short int a1, b1, c1 ; // declare the variable a1, b1 and c1 as of short integer type  (normally 2 byte)
  long int  a2, b2, c2 ; // declare the variable a2, b2 and c2 as of long integer type  (normally 4 or 8 byte)

  float  C ; // declare C as a single precision variable (4 byte normally)
  double D ; // declare D as a double precision variable (8 byte normally)
  
  char   a3, a4 ; // declare a3 and a4 as charater (1 byte)
  
  unsigned short int aa, bb, cc ; // declare the variable aa, bb and cc 
                                  // as of short integer type without sign (normally 2 byte)

  // the prefix short and long can be used to define the size of integer
  // the prefix signed, unsigned can be used for int and char

  ;;;;;; // ; is a separation characted ;; separate EMPTY instructions

  printf("ciao mamma\n") ; // \n is the new line character
  
  // some instruction for conditional execution
  C = 1.0 ;
  D = 1.3 ;
  if ( C == D )
    printf( "C and D are equal\n" );
  else
    printf( "C and D are NOT equal\n" );
  
  if ( C = D ) printf( "C = D is true but it is really false!\n" ) ;
  
  // some loop intruction
  int i=10 ; // declare i as intger and initialize to 10
  // while ( expr )  intruction ;
  // when expr is different from 0 or true execute "intruction"
  while ( --i ) printf( "%d\n", i ) ;
  // --i means i = i-1 the operation is performed before the value of i is used
  i = 10 ; // re-initialize i to 10
  while ( i-- ) printf( "%d\n", i ) ;
  // i-- means i = i-1 the operation is performed after the value of i is used
  
  
  // for ( init ; expr ; incr ) instruction ;
  // is equivalent to
  // init ; // executed only one time at the beginning
  // while ( expr ) { intruction ; incr }
  //
  // the 
  //   while(expr) instr ;
  // loop is equivalent to 
  //   for ( ; expr ; ) instr ;
  //
  // infinite loop 
  //   while (1) expr ;
  //   for (;;) expr ;
  
  for ( int j = 1 ; j < 10 ; j *= 2 ) { // j *= 2 ==> j = j*2 ;
                                        // in general res OP= expr ==> res = res OP expr
                                        // where OP can be + - / * ~ | &
    printf( "for loop, i = %10d\n", j) ;
  }
  
  // do { ... } while () is near the same of while loop
  //
  unsigned ii=10 ;
  do {
    printf( "do while loop i = %u\n", ii ) ;
  } while ( --ii > 0 ) ;
  
  // the last conditional instruction is switch
  //
  //  switch ( integer expressin ) {
  //    case NUMBER:
  //      inst ;
  //       ....
  //      inst ;
  //      [ break ; ]
  //    case NUMBER:
  //      inst ;
  //       ....
  //      inst ;
  //      [ break ; ]
  //      ....
  //     [ default: ]
  //      inst ;
  //       ....
  //      inst ;
  //      [ break ; ]
  //  }
  //
  for ( i=0 ; i < 10 ; ++i ) {
    switch ( i ) {
      case 0:  printf("pass 0, i=%d\n",i) ; break ;
      default: printf("pass default, i=%d\n",i) ;
      case 1:  printf("pass 1, i=%d\n",i) ;
      case 4:  printf("pass 4, i=%d\n",i) ; break ;
      case 5:
      case 6:
      case 7:
        printf("pass 5,6,7, i=%d\n",i) ; break ;
    }
  }

  return 0 ; // exit from the program, all thing go well
}

Print first N numbers

File myinclude.h

int pippo() ; // declare a body of a function

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