Lesson of 15 February 2010

Some simple C/C++ programs

A minimal program

File example1.cc

 1/*
 2  I am a comment
 3 */
 4 
 5// I am a single line comment
 6
 7/*
 8   A C/C++ program is a "function" called "main()"
 9   which return an integer.
10   Return 0 means all ok!.
11   Return != from 0 signal an error to the OS
12 */
13
14// standard I/O of C (libc) 
15#include <stdio.h>
16
17// standard I/O of C++ (libstdc++) 
18#include <iostream>
19
20using std::cout ; // use object cout of namespace std
21using namespace std ; // use all the functions and object of namespace std
22
23int // the type of return value
24main() { // brackets contains the bosy of the program
25  
26  // standard C way of I/O
27  printf("I am a string\n") ; // \n = new line character
28                              // \r = return character
29                              // \t = tabulation
30  // cout = character out object                        
31  cout << "I am a string output by cout\n" ;
32
33  return 0 ; // return 0 to the OS
34}

Built in types

File example2.cc

 1// standard I/O of C (libc) 
 2#include <stdio.h>
 3
 4// standard I/O of C++ (libstdc++) 
 5#include <iostream>
 6
 7using namespace std ; // use all the functions and object of namespace std
 8
 9int // the type of return value
10main() { // brackets contains the bosy of the program
11  
12  // the standard type of C/C++
13  int a, b, c ; // declare and define a, b, c as integer variable
14  c = 1 ;
15  a = 1 ; // assign a to the value 1
16  a = b / c ; // integer division
17  a = b % c ; // remainder of the division of b by c
18  /*
19     other integer like type
20     short int (smaller integer normally 2 byte)
21     long  int (larger integer normlly 8 byte)
22     
23     unsigned int (int without sign)
24     unsigned short int (short int without sign) [ short == short int]
25     unsigned long int (long int without sign)   [ long  == long int]
26   */
27
28  float d, e, f ; // declare and define d, e,f as single precision floating point variables
29  d = 1.0 ;
30  e = 2.0 ;
31  e += d ; // ==> e = e + d 
32           // in general "a OP= b" is equivalent to " a = a OP b "
33  
34  double g, h, i ; // declare and define d, e,f as double precision floating point variables
35
36  return 0 ; // return 0 to the OS
37}

Conditional and loops

File example3.cc

 1// standard I/O of C (libc) 
 2#include <stdio.h>
 3
 4// standard I/O of C++ (libstdc++) 
 5#include <iostream>
 6
 7using namespace std ; // use all the functions and object of namespace std
 8
 9int
10main() {
11  
12  int a, b, c, d ;
13  
14  a = 1 ;
15  if ( a < 3 ) cout << " a < 3 " ;
16  else         cout << " a >= 3 " ; // use {} or more than 1 instruction
17  /* 
18    comparisoin operators
19    == Check equality
20    != Check inequality
21    > greather then
22    < less then
23    >= greather or equal then
24    <= less or equal then
25  */
26  
27  if ( a<3 && b == 0 ) cout << "a<3 and b==0\n" ;
28  /*
29    logical operation
30    
31    || or
32    && and
33    ! not
34  */  
35  
36  for ( int i=0 ; i < 10 ; ++i ) // ++i => i = i+1
37    cout << i << "\n" ; 
38  
39  /*
40    for ( A ; B ; C ) EXPR ;
41    
42    A is executed ONCE at the beginning of the loop
43    B is execued EACH time at the beginning of the loop
44    EXPR is executed each time B is true
45    C    is executed at the end of each loop
46  */
47  
48  int i = 10 ;
49  while ( --i > 0 ) cout << i << "\n" ;
50  /*
51    while ( A ) EXPR ;
52    EXPR is executed each time A is true
53  */
54  
55  i = 10 ;
56  do {
57    cout << i << "\n" ;
58  } while ( --i > 0 ) ;
59  /*
60    do { EXPR ; } while ( A ) ;
61    EXPR is executed, then check A
62   */
63
64  return 0 ; // return 0 to the OS
65}

Functions and recursion

File example4.cc

 1// standard I/O of C (libc) 
 2#include <stdio.h>
 3
 4// standard I/O of C++ (libstdc++) 
 5#include <iostream>
 6
 7using namespace std ; // use all the functions and object of namespace std
 8
 9// define the function factorial
10int
11fact( int n ) {
12  int res = 1 ;
13  for ( int i = 2 ; i <= n ; ++i )
14    res *= i ;
15  return res ;
16}
17
18// define the function factorial recursively
19int
20factRec( int n ) {
21  if ( n <= 1 ) return 1 ;
22  return n* factRec(n-1) ;
23}
24
25
26int
27main() {
28  int n = 4 ;
29  cout << "fact " << n << " = " << fact(n) << "\n" ;
30  cout << "factRec " << n << " = " << factRec(n) << "\n" ;
31  return 0 ; // return 0 to the OS
32}

Splitting code in more files

File example5.h

 1// standard I/O of C (libc) 
 2#include <stdio.h>
 3
 4// standard I/O of C++ (libstdc++) 
 5#include <iostream>
 6
 7using namespace std ; // use all the functions and object of namespace std
 8
 9// declaration the function factorial
10extern int fact( int n ) ;
11
12// define the function factorial recursively
13extern int factRec( int n ) ;

File example5.cc

 1// standard I/O of C (libc) 
 2#include "example5.h"
 3
 4int
 5main() {
 6  int n = 4 ;
 7  cout << "fact " << n << " = " << fact(n) << "\n" ;
 8  cout << "factRec " << n << " = " << factRec(n) << "\n" ;
 9  return 0 ; // return 0 to the OS
10}

File example5b.cc

 1// standard I/O of C (libc) 
 2#include "example5.h"
 3
 4// define the function factorial
 5int
 6fact( int n ) {
 7  int res = 1 ;
 8  for ( int i = 2 ; i <= n ; ++i )
 9    res *= i ;
10  return res ;
11}
12
13// define the function factorial recursively
14int
15factRec( int n ) {
16  if ( n <= 1 ) return 1 ;
17  return n* factRec(n-1) ;
18}