Advanced Introduction to C++, Scientific Computing and Machine Learning




Claudius Gros, WS 2021/22

Institut für theoretische Physik
Goethe-University Frankfurt a.M.

C++ : Data Types


primitive data types

Typ Size Domain Example
bool 1 {true, false} bool b = true;
char 1 [0x0000, 0xFFFF] char c = 'a';
byte 1 [−27, 27−1] = [−128, 127] byte b = 4;
short int 2 [−215, 215−1] = [−32,768, 32767] short int s = 12345;
int 4 [−231, 231−1] =
[−2,147,483,648, 2,147,483,647]
int i = 17;
long int8 [−263, 263−1] long int l =8L;
float 4 [1.40239846 ⋅ 10–45, 3.40282347 ⋅ 1038] float f = 3.14F ;
double 8 [4.94065645841246544 ⋅ 10–324,
1.79769131486231570 ⋅ 10308]
double d = 3.14

example: primitive data types

Copy Copy to clipboad
Downlaod Download
#include <iostream>
#include <stdio.h>
#include <complex>  // complex numbers
using namespace std;

int main()
{
 int intArray[5] = { 16, 2, 77, 40, 12071 }; 
 double doubleArray[10];
//
 printf("size of        bool   : %4d\n",(int)sizeof(bool));
//
 printf("size of        char   : %4d\n",(int)sizeof(char));
 printf("\n");
 printf("size of        int    : %4d\n",(int)sizeof(int));
 printf("size of  short int    : %4d\n",(int)sizeof(short int));
 printf("size of   long int    : %4d\n",(int)sizeof(long int));
 printf("\n");
 printf("size of        float  : %4d\n",(int)sizeof(float));
 printf("size of        double : %4d\n",(int)sizeof(double));
 printf("size of   long double : %4d\n",(int)sizeof(long double));  // what is that?
 printf("\n");
 printf("size of      intArray : %4d\n",(int)sizeof(intArray)); 
 printf("size of   doubleArray : %4d\n",(int)sizeof(doubleArray));
//
 typedef complex<double> doubleComplex;
 printf("\n");
 printf("size of doubleComplex : %4d\n",(int)sizeof(doubleComplex)); 
 printf("\n");
//
//
 printf("=== =============================== ===\n");
 printf("=== having fun with complex numbers ===\n");
 printf("=== =============================== ===\n");
 doubleComplex a(1.11,2.22),b(0,1);
 printf("\n");
 printf("a         = %f + %f i\n",a.real(),a.imag());
 printf("\n");
//
 cout << "a         = " << a       << "\n";
 cout << "b         = " << b       << "\n";

 cout << "a + b     = " << a + b   << "\n";
 cout << "a * b     = " << a * b   << "\n";
 cout << "a / b     = " << a / b   << "\n";
 cout << "|a|       = " << abs(a)  << "\n";

 cout << "a*        = " << conj(a) << "\n";
 cout << "norm(b)   = " << norm(b) << "\n";
 cout << "exp(b*pi) = " << exp(b*M_PI)  << "\n";  // check precision !
 printf("\n");
 printf("pi        = %50.48f\n",M_PI);

 return 0;
}

type conversion vs casting

Copy Copy to clipboad
Downlaod Download
#include <iostream>
#include <stdio.h>
#include <typeinfo>    // typeinfo
using namespace std;

int main()
{
//                 implicit type conversion
 short a=2000;
 int b;
 b=a;
 printf("a = %5d,  b = %5d\n",a,b);
 printf("\n");
//
//                 explicit type conversion
//
 double x = 10.3;
 int y,z;
 y = int(x);    // functional notation
 z = (int)x;    // c-like cast notation 
 printf("x = %6.3f,  y = %3d,  z = %3d\n",x,y,z);
 printf("\n");
//
//                 type checking
//
 if (typeid(a) != typeid(b))
   {
    cout << "a and b are of different types:\n";
    cout << "a is: " << typeid(a).name() << '\n';
    cout << "b is: " << typeid(b).name() << '\n';
  }
//
//                 converting to strings using to_string
//
 double myDouble = 0.3141;
 printf("\n");
 printf("number = %6.4f,  strResult = %s\n", myDouble, 
        to_string(myDouble).c_str());
//
//                 converting to strings via a string stream
//
 int myInt = 123;      
 printf("\n");
 char strResult[16];                               // string  (array of char)
 sprintf(strResult, "%d %6.4f", myInt, myDouble);  // write to array of char
 printf("number = %d,  strResult = %s\n", myInt, strResult);
//
//                 converting from strings
//
 char text[] = "456";  // string to be converted
 int intResult;        // number which will contain the result
 sscanf (text,"%d",&intResult);        // pointer: &intResult
 printf("  text = %s,  intResult = %d\n",text,intResult);
//
//                 ASCII character table
//
 printf("\n");
 printf("=== ===================== ===\n");
 printf("=== ASCII character table ===\n");
 printf("=== ===================== ===\n");
 printf("\n");
 for ( int x = 0; x < 128; x++ ) 
   cout << x << ". "<< (char)x << "\n"; 
 printf("\n");
//
 return 0;
}

arithmetic operators

SymbolDescriptionExamples
=assignment int i=5;
+  -addition, subtraction int i=5+3; int i=5-3;
*  /multiplication, integer division int i=5*3; int i=9/3;
%modulo int i=14%3;
+  -unary plus/minus int i=+3; int i=-2;
+=  -=  *=   /=assignment and operation i += 5; // i = i + 5
++   --pre-/postfix increment/decrement i++; // i = i + 1

Copy Copy to clipboad
Downlaod Download
#include <iostream>
using namespace std;

int main()
{
  int myInt = 0;
  cout << "0: myInt " << myInt   << endl;
//
  ++myInt;
  cout << "1: myInt " << myInt   << endl;
//
  myInt++;
  cout << "2: myInt " << myInt   << endl;
//
  cout << "3: myInt " << ++myInt << endl;
//
  cout << "4: myInt " << myInt++ << endl;
  cout << "5: myInt " << myInt   << endl;
//
  return 0;
}

mathematical functions

Copy Copy to clipboad
Downlaod Download
#include <iostream>
#include <math.h>
using namespace std;

int main()
{
  double number,dsqrt,dpow,dlog,dlog10,expLog;

  cout << "Please enter a number \n";
  cin >> number;

  dsqrt  = sqrt(number);
  dpow   = pow(number,3);
  dlog   = log(number);
  dlog10 = log10(number);
  expLog = log(exp(number));


  cout << "\n";
  cout << "square root of  " << number << "   is : " 
       << dsqrt << "\n";
  cout << "        log of  " << number << "   is : " 
       << dlog << "\n";
  cout << "      log10 of  " << number << "   is : " 
       << dlog10 << "\n";
  cout << "                " << number << "^3 is : " 
       << dpow << "\n";
  cout << " exp of log of  " << number << "   is : " 
       << expLog << "\n";

  return 0;
}

arrays

example: arrays

Copy Copy to clipboad
Downlaod Download
/* compile with  g++             -o test.e test.c  */
/*      or with  g++    -DNDEBUG -o test.e test.c  */
/*                      (turns `assert()' off)     */
//
#include <iostream>         // input/output handling
#include <stdio.h>          // for formatted input/output
#include <assert.h>         // (`assert()' calls abort if arg not true)
#define VARIABLE_NAME(x) #x     // a C++ macro definition
using namespace std;

int main()
{
 int badHabit[10];             // generically bad programming
 const int arrayLength = 10;   // array length need to be constant
 int goodHabit[arrayLength];   // much better programming
//
 cout << "goodHabit has " << sizeof(goodHabit) / sizeof(goodHabit[0])
      << " elements\n\n";
//
 goodHabit[0] = 0;                 // first element
 for (int i=1;i<arrayLength;i++)   // starting at second element
   goodHabit[i] = goodHabit[i-1]+1;
 for (int i=0;i<arrayLength;i++)   
   cout << VARIABLE_NAME(goodHabit) 
        << "[" << i << "] = "
        << goodHabit[i] << "\n";
 printf("=== ==================== ===\n");
 printf("=== array bound checking ===\n");
 printf("=== ==================== ===\n");
 string stringArray[] = {"apple","banana","oranges"};
 for (int i=0;i<6;i++)   
   {
   assert(i>=0);     // array size checking by hand
   assert(i<sizeof(stringArray)/sizeof(string));
   printf("stringArray[%d] = %s\n",i,stringArray[i].c_str());
   }
 return 0;
}

example: matrices

Copy Copy to clipboad
Downlaod Download
#include <iostream>  // input/output handling
#include <stdio.h>   // for formatted input/output
using namespace std;
 
const int X=9;
const int Y=7;
 
int main()
{
 char Spielfeld[Y][X];
 int x, y;
 char cx, cy;
 for (x=0; x<X; x++)
   for (y=0; y<Y; y++)
     Spielfeld[y][x] = '.';
//
// Anzeige und Eingabe
//
  bool SchleifenEnde=false;
  int xin, yin;
  do {
     printf("  ");
     for (x=0; x<X; x++)
       printf("%3d",x+1);
     printf("\n");
//
     for (y=0; y<Y; y++)
       {
       cout << (char)('A'+y) << " ";
       for (x=0; x<X; x++)
         printf("%3c",Spielfeld[y][x]);
       cout << endl;
       }
//
  cout << "your hit: ";
  cin >> cy >> cx;
  xin = cx - '1';
  yin = cy - 'A';
  if (xin>=0 && xin<X && yin>=0 && yin<Y)
    {
    Spielfeld[yin][xin] = 'x';
    cout << "# (yin,xin): (" << yin
         << "," << xin
         << ")\n\n";
    }
   else
    SchleifenEnde = true;
    } while (!SchleifenEnde);
}

example: strings

Copy Copy to clipboad
Downlaod Download
#include <iostream>
using namespace std;

int main() {
  string str1 = "To be or not to be, that is the question";
  string str2 = "only ";
  string str3 = str1.substr(6, 12);
//                    // endl == end of line
  cout << "str1        :: " << str1 << endl; 
  cout << "str2        :: " << str2 << endl; 
  cout << "str3        :: " << str3 << endl; 
  cout << "str2 + str3 :: " << str2+str3 << endl;
//
  cout << "str1 (again)         :: " << str1 << endl;
  str1.insert(32, str2);
  cout << "str1 (after insert)  :: " << str1 << endl;
  str1.replace(str1.find("to be", 0), 5, "to jump");
  cout << "str1 (after replace) :: " << str1 << endl;
  str1.erase(9, 4);
  cout << "str1 (after erase)   :: " << str1 << endl;
//        
  for (int i = 0; i < str3.length(); i++) // accessing the length
    cout << str3[i]; 
  cout << endl;
//           
  cout << "str3 (again)         :: " << str3 << endl;
  cout << "str3.length()        :: " << str3.length() << endl;
  str3.clear();
  cout << "str3 (after clear)   :: " << str3 << endl;
}