// Here we can see that more than one variables
// are being used without reporting any error.
// That is because they are declared in the
// different namespaces and scopes.
#include
using namespace std;
// Variable created inside namespace
namespace first
{
int val = 500;
}
// Global variable
int val = 100;
int main()
{
// Local variable
int val = 200;
// These variables can be accessed from
// outside the namespace using the scope
// operator ::
cout << first::val << ‘\n’;
return 0;
}
C++[] –> namespace is like a named-scope, so you can use it kind of like everywhere
CNU library
https://www.gnu.org/software/libc/manual/html_node/Getopt.html
More about C/C++ library
https://www.tutorialspoint.com/c_standard_library/index.htm
https://www.tutorialspoint.com/cpp_standard_library/index.htm
Two way to manipulate string.
std::string
| String Object | C-Style Sting |
| #include "string" | #include "cstring" / "string.h" |
| string myStr = "Hello World"; | char myCharr[20] = "Hello World"; |
| str1 = str2; | strcpy(charr1, charr2); |
| str1 += str2; | strcat(charr1, charr2); |
| str.size() | strlen(charr) |
| getline(cin, str); | cin.getline(charr, 20); //20 - max len |
int myVar = 8; // variable myVar store value
&myVar; //address of myVar
int *myPtr;
myPtr = &myVar; // pointer myPtr store address of myVar
*myPtr; //value of the address pointed by myPtr
| myVar | &myVar |
| *myPtr | myPtr |
| value => 23 | address => 0x1234 |
int size; cin >> size;
int * pz = new int [size]; // dynamic binding, size set at run time
…
delete [] pz; // free memory when finished
| 1 | 2 |
| void swapr(int & a, int & b) // use references { int temp; temp = a; // use a, b for values of variables a = b; b = temp; } | swapr(wallet1, wallet2); // pass variables |
| void swapp(int * p, int * q) // use pointers { int temp; temp = *p; // use *p, *q for values of variables *p = *q; *q = temp; } | swapp(&wallet1, &wallet2); // pass addresses of variables |
| void swapv(int a, int b) // try using values { int temp; temp = a; // use a, b for values of variables a = b; b = temp; } | swapv(wallet1, wallet2); // pass values of variables |