C++_class_powerpoint_1.1

Types and Declarations

Boolean Type

bool type – boolean , logic type
bool literal – true, false
int and bool

• Nonzero->true
• Zero ->false
• true ->1
• false->0

1 <= sizeof( bool) <= sizeof(long)

void f(int a,int b)
 {
    bool b1{a==b}; 
    bool b2 = a==b;
    …
 }

 bool isGreater(int a, int b){return a > b;} 

void f()
{
    bool a=true,
           b=true;
    bool x=a+b;
    bool y=a||b;
}   

Knowing Ranges of Types

// Implementation-dependent
#include <limits>
int main()
{
   cout << "largest integer = " 
    << numeric_limits<int>::max();
   cout << “smallest integer = " 
    << numeric_limits<int>::min();
   return 0; 
}

Binary Literal

int a=0b1100,b=0B0101;

::globalId can be used in a local scope, even its name is identical to local one.

int x;
void f()
{
    int x=1;
    ::x=2;
    x=3;
    …
}//::x means the x is the global one

int x=1;

void f(){

    int x=2;
    ::x=3;
    printf("%d ",x);

}

int main()
{
    f();
    printf("%d",x);
    return 0;
}//output 2 3

auto

If the type of a variable can be deducted from its initialization, keyword auto can be used instead of type name in the definition.

auto i{0};
vector<string> v; …
   for (const auto& x : v) cout << x << '
';
for (auto i : {1, 2, 3, 4, 5, 6, 7}) 
       cout << i << '
';

Initialization

four syntactic styles:

• T a1 {v};
• T a2 = {v};
• T a3 = v;
• T a4(v);

Pointers, Arrays and Structures

Variable-size arrays

#include <vector>
using namespace std;
void f(int i)
{
    vector<int> v1(i);
    vector<int> v2{1,2,3};
    vector<int> v3(i,10);
    …
}

Constants

Keyword const as a modifier

• A constant identifier must be initialized and cannot be assigned
• Prefer to #define macro usage
• Using symbolic constants is better than using literals in the large programs

 

Pointers and Constants

Prefixing a pointer with const makes an object the pointer points to, not pointer itself, a constant.

const int someInt=10;
   const int *p = &someInt; 
//Or
   int const  *p = &someInt; 
  // *p is a constant, p is a variable

To declare a pointer itself to be a constant, use the declarator *const .

int someInt=10;
int *const p = &someInt; 
// p is a constant

To declare both the pointer and the object the pointer points to  be constants, use two const modifiers.

const int someInt=10;
const int *const p = &someInt; 
//Or
int const *const p = &someInt; 
// *p is a constant, p is a constant too.

void f4( )
{  int a=1;
    const int c=2;
    const int* p1=&c; 
    const int* p2=&a; //non const ptr  const ptr
    int * p3=&c; // Error! 
    *p3=7;           
}
// a non-constant pointer can assign to a constant
// pointer, but a constant pointer cannot assign to
//  a non-constant pointer.

References

A reference is alias/nickname for an object or a function.

The main usages:
      1. specifying arguments and return values
          for functions 
      2. for overloaded operators.
Notation : Typename&
References must be initialized.

void f()
{
    int i=1;
    int& r{i};
    int x=r;
    r=2;
}//Both i and r are occupied the same memory

constant references

Constant Reference can refer to a non lvalue or other type object.
For const T&,
   [1] implicit conversion to T if necessary
   [2] result is placed in a temporary object
   [3] reference to the temporary object
The temporary object persists until the end of its reference's lifetime.

References as Parameters of Functions

The function can change the value of an object passed to it.
This is called call-by-reference passing mechanism. It is different from call-by-value.

void increment(int& a) 
{ a++; } //x++
void f()
{
    int x=1;
    increment(x); // x==2
}//Parameter a is initialized with the argument x

The return value of the function can refer to the expression of return statement.

struct Pair{
    string name;
    double val;
};

vector<Pair> pairs;
double& value(const string& s)
{
    for (auto& x: pairs)
        if (s==x.name) return x.val;//original val+1;
    pairs.push_back({s,0});
    return pairs.back().val;//0->1
}

int main()
{  
   for (string buf; cin>>buf;)
    // enter ^d in Linux at end of the input
          value(buf)++;  
   for (const auto& x: pairs)
       cout << x.name << ": " 
          << x.val  << '
';
   return 0; 
}

void*

Pointer to any data type(not function type)
Be able to assign, compare and cast to another pointer type
 T*　-->void* is type coercion
void*-->T* must use type cast

int i=100;
void* pv=&i; // type coercion
int* pi1 = static_cast<int*>(pv);
int* pi2 = (int*)pv;

Structure type name

Typename of a structure is structure tag , keyword struct is unnecessary.
For example:
      struct address {…};
      type name is address,
      but struct address in C.

Structure forward declaration

The typename of a structure is available for use as pointer to structure immediately after it has been encountered and not just after the complete declaration has been seen.

 struct Link{ Link* next; … }; 

To allow two or more types refer to each other, use structure forward declaration.

 struct List; struct Link{ List* a; … }; struct List{ Link* a; … };