Chapter 2 ¶
μ€μ μμ€ ¶
~cpp
#include <iostream>
#include <string>
// say what standard-library names we use
using std::cin;
using std::cout;
using std::string;
using std::endl;
int main() {
// ask for person's name
cout << "Please enter your first name: ";
// read the name
string name;
cin >> name;
// build the message that we intend to write
const string greeting = "Hello, " + name + "!";
// the number of blacks surrounding the greeting
const int pad = 1;
// the number of rows and columns to write
const int rows = pad * 2 + 3;
const string::size_type cols = greeting.size() + pad * 2 + 2;
// write blank line to separate the output from the input
cout << endl;
// write rows
// invariant: we have written r rows so far
for (int r = 0; r != rows ; ++r) {
string::size_type c = 0;
// invariant: we have written c
while (c != cols) {
// is it time to write the greeting?
if (r == pad + 1 && c == pad + 1) {
cout << greeting;
c += greeting.size();
} else {
// are we on the border?
if (r == 0 || r == rows - 1 ||
c == 0 || c == cols - 1)
cout << "*";
else
cout << " ";
++c;
}
}
cout << endl;
}
return 0;
}
----
μ§λ¬Έ ¶
μ±
μ 보면 (21νμ΄μ§),
----
~cpp
// invariant : we have written r rows so far
int r = 0;
// setting r to 0 makes the invariant true
while( r != rows )
{
// we can assume that the invariant is true here
// writing a row of output makes the invariant false
std::cout << std::endl;
// incrementing r makes the invariant true again
++r;
}
// we can conclude that the invariant is true here
μ½λμ λ§μ§λ§ λΆλΆμμ invariant κ° λ€μ true λ‘ λλκ²μΌκΉμ.? invariant κ° λ¬΄μμΈμ§ μμ§ κ°λ
μ΄ μ‘νμ§ μμμ. -_-a - μμΈν
μ λ μ΄μ μμΌ AcceleratedC++μ λ³΄κ³ μλλ°μ. loop invariantλ rλ² μννλ€λΌλ κ²μ λ§νμ§ μμκΉμ?
rμ΄ μ²μμ 0μ΄λκΉ whileμ μ§μ νλ μμ μλ coutμ 0λ² μννμν κ³ λ°λΌμ r = 0, μννμ = 0 λ°λΌμ λΆλ³μμ μ°Έ
rμ΄ 0μ΄κ³ coutμ νλ² μννλ©΄ r = 0, μννμ = 1 λ°λΌμ λΆλ³μ κ±°μ§
whileμ λ§μ§λ§ μ μ rμ 1 μ¦κ°μν€λ―λ‘... r = 1, μννμ = 1 λ°λΌμ λΆλ³μ μ°Έ
λ°λΌμ whileμ 쑰건μ λΉκ΅μμλ r = 1, μννμ =1 λ°λΌμ λΆλ³μ μ°Έ...
λ cout μ μννκ² λλ€λ©΄ r = 1, μννμ = 2λκΉ λΆλ³μ κ±°μ§...
μμ μ http://www.pragmaticprogrammer.com/ppllc/papers/1998_05.html μμ invariantsλΌλ λ§μ΄ λμμλλ° κ°μ κ°λ μΌλ‘ μκ°νλ©΄ λ λ €λ γ ‘,.γ ‘; --Benghun
rμ΄ μ²μμ 0μ΄λκΉ whileμ μ§μ νλ μμ μλ coutμ 0λ² μννμν κ³ λ°λΌμ r = 0, μννμ = 0 λ°λΌμ λΆλ³μμ μ°Έ
rμ΄ 0μ΄κ³ coutμ νλ² μννλ©΄ r = 0, μννμ = 1 λ°λΌμ λΆλ³μ κ±°μ§
whileμ λ§μ§λ§ μ μ rμ 1 μ¦κ°μν€λ―λ‘... r = 1, μννμ = 1 λ°λΌμ λΆλ³μ μ°Έ
λ°λΌμ whileμ 쑰건μ λΉκ΅μμλ r = 1, μννμ =1 λ°λΌμ λΆλ³μ μ°Έ...
λ cout μ μννκ² λλ€λ©΄ r = 1, μννμ = 2λκΉ λΆλ³μ κ±°μ§...
μμ μ http://www.pragmaticprogrammer.com/ppllc/papers/1998_05.html μμ invariantsλΌλ λ§μ΄ λμμλλ° κ°μ κ°λ μΌλ‘ μκ°νλ©΄ λ λ €λ γ ‘,.γ ‘; --Benghun
μ΄μ§Έμ Cμ 루νλ0λΆν°? μΈμ§... κ°λ¨ν λλ΅μ΄ λμ μλκ΅°μ. - ν±μ보λ€
AcceleratedC++










