Review

第一階段複習

Jason

Content

Type, Variable, and Operator
Flow Control
Array & C-Style String
Pointer
Function

上週作業講解

void solve(char message[]) {
    srand(time(NULL));
    encrypt(message, t - (rand() % 1000));
    cout << message;
}

Can we assume the time() will return the same value?

Then we can get the same random values from rand()

Type, Variable, and Operator

Type 變數型別

int, char, long long, float, ...

Variable 變數

type variableName (= initialValue);

int test = 10;
char c = 'a';
long long l = 2147483648;

c = 'k';

Type, Variable, and Operator

Operator 運算子

int a;

cin >> a; // read integer from stdin
cout << a + 50 << endl; // output result to stdout

a += 10;
a -= 20;
a /= 5;
a *= 10;

Quick Question: How many operators in above?

Flow Control

Conditions （條件判斷）

bool cond1 = {...}; 
bool cond2 = {...};

if(cond1) {
  // cond1 = true
  if (cond2){
    // cond2 = true
  } else {
    // cond2 = false
  }
} else if(cond2) {
  // cond1 = true & cond2 = false
} else {
  // cond1 = false & cond2 = false
}

Can be Nested / Conditions are evaluated as boolean

Flow Control

Loops

int i = 0;
while(i < 10){
  cout << i << endl;
  i++;
}

for(int i = 0; i < 10; i++){
  cout << i << endl;
}

for(int i = 0; i < 10; i++){
	for(int j = 0; j < i; j++)
    	cout << "*";
    cout << endl;
}

Quick Question: Can all for-loop be translated to while-loop

Quick Question: Can all while-loop be translated to for-loop

Array & C-Style String

Array: Multiple items of same type

int arr1[10] = {1,2,3,4};
int arr2[] = {3,4,5,6,7};
char arr3[] = "Hello?";

double arr4[105];
for(int i = 0; i < 105; i++)
  cin >> arr4[i];

int arr2D[10][20];

for(int i = 0; i < 10; i++)
  for(int j = 0; j < 20; j++)
    arr2D[i][j] = i * j;

How many indices allocated in above code?

Array & C-Style String

C-Style String: Basically char array ended with '\0'

char s1[] = "Hello?";
char s2[10];

strcpy(s2, s1);
cout << s2 << endl;

cout << strlen(s2) << endl;

// print ascii value for each char in s2
for(int i = 0; s2[i]; i++)
  cout << (int)s2[i] << endl;

// concat two string
char sa[] = "???";
strcat(s2, sa);
cout << s2 << endl;

The size of s1 array is?

Pointer

Variable that points to variable address

int a = 10;
int *ptr = &a;
cout << ptr << " " << *ptr << endl;

*ptr = 20;
cout << ptr << " " << *ptr << " " << a << endl;

int b = 20;
ptr = &b;
*ptr = 30;
cout << a << " " << b << " " << *ptr << " " << ptr << endl;

int arr[10] = {1,2,3,4,5,6,7,8,9,10};
cout << *(arr+5) << " " << arr[5] << endl;

What will be the output?

Function

A way to modularize procedures

// passing parameters by value / address / reference
int addA(int a, int *arr, int n){
  for(int i = 0; i < n; i++)
    arr[i] += a;
}

// swap(&a, &b);
void swap2(int *a, int *b){
  int tmp = *a;
  *a = *b;
  *b = *a;
}

// swap(a, b);
void swap1(int &a, int &b){
  int tmp = a;
  a = b;
  b = a;
}

Return type / Parameter type / Passing by value, address or reference