Block Collection

定义(声明) 和 赋值变量

	对或者错，错误原因
int 3;	cannot start with digit int a=3;
double;	double b;
int = 19;	int c=19;
float myten = 10.23;	正确
double_sum = 2.2;	double sum = 2.2;
int that_value 212;	int that_value = 212;

Invalid variable naming	Valid variable naming	Description
int monthly income	int monthly_income	Monthly income of integer type
---	int counter**;**	Counter of integer type
double %scale	double scale**;**	Scale of double type
---	double bike_sales**;**	Sales of bike of double type

Program Segment	User input	Answer
int first, second, third;cin >> first >> second >> third;	24 25 26	正确
double fourth, fifth, sixth;cin >> fourth >> fifth >> sixth;	24.4 25.5 26	正确
int seventh, eighth, ninth;cin >> seventh >> eighth >> ninth;	24.4 25.5 26.6	×
double tenth, eleventh, twelfth;cin >> tenth >> eleventh >> twelfth;	23.4 24.5	×

提示：长位向段位兼容

Program Segment	Answer
int d = 4;	√
double a; int d = d * (6 + d);	×
double d = "3";	×

计算语句

Program Segment	Answer
int z = 9 + 2;	11
int z = 9 - 2;	7
int z = 5 * 2;	10
int z = 8 / 4;	2
int z = 9 / 4;	2
double z = 9 / 4;	2
int z = 222 / 300;	0
double z = 222.0 / 300.0;	0.74
int z = 222 / 300.00;	0
double z = pow(3, 6);	729

常用代码

数组从大到小排序

#include <iostream> 
#include <iomanip>
using namespace std; 

int main() {
	const int ARRAY_SIZE = 10;
	int data[ARRAY_SIZE] = { 2, 64, 4, 33, 10, 12, 89, 68, 45, 7 };
	int i, insert;
	cout << "Data items in original order\n"; 
  
	for (i = 0; i < ARRAY_SIZE; i++) {
		cout << setw(4) << data[i];
	}
  
	for (int next = 1; next < ARRAY_SIZE; next++) { 
		insert = data[next];
		int moveItem = next;

		while ((moveItem > 0) && (data[moveItem - 1] < insert)) { // 改成大于号后变成由小到大排序
    	data[moveItem] = data[moveItem - 1];
			moveItem--;
  		}
    
		data[moveItem] = insert;
	}
  
	cout << "\nData items in new order\n"; 
  for (i = 0; i < ARRAY_SIZE; i++) {
		cout << setw(4) << data[i];
  	}
  
	cout << endl; 
  return 0;
}

统计一个范围内的质数个数

Counting Prime Numbers

#include <iostream>
using namespace std;

bool isPrime(int n) {
  for (int i = 2; i < n; i++) {
    if (n % i == 0) {
      return false; 
    } 
  }
  return true; 
}

int countPrime(int n) {
  // base case
  if (n == 2) {
    return 1;
  }
  // general case
  if (isPrime(n)) {
    return countPrime(n - 1) + 1;
  } else{
    return countPrime(n - 1);
  } 
}

int main() {
int input;
cout << "Please enter an integer: "; 
cin >> input;
cout << "Total number of prime between 1 and " << input << " is " << countPrime(input) << "." << endl; 
}

三目运算

#include <stdio.h>
#include <iostream>
using namespace std;
int main()
{
	int a=0, b=3, c=2;
	a = (b > c ? b : c);      //b大于c，所以a=b=3
	cout << "a=" << a << endl;
}

#include <stdio.h>
#include <iostream>
using namespace std;
int main()
{
	int a=0, b=1, c=2;
	a = b > c ? b : c;      //b小于c，所以a=c=2
	cout << "a=" << a << endl;    
}

Call by Pointer

#include <iostream>
using namespace std;


void swp(long* xp, long* yp){
    long t0 = *xp;
    long t1 = *yp;
    *xp = t1;
    *yp = t0;
}


int main() {
    long x=1,y=2;
    swp(&x,&y);
    cout << x << " " << y << "\n";

    return 0;
}

size of()

#include <iostream>
using namespace std;

int main()
{
    cout << "Size of char : " << sizeof(char) << endl;
    cout << "Size of short : " << sizeof(short) << endl;
    cout << "Size of int : " << sizeof(int) << endl;
    cout << "Size of long  : " << sizeof(long) << endl;
    cout << "Size of float : " << sizeof(float) << endl;
    cout << "Size of double : " << sizeof(double) << endl;
    cout << "Size of long double : " << sizeof(long double) << endl;
    cout << "Size of bool : " << sizeof(bool) << endl;
    return 0;
}

结果（单位为byte）

Size of char : 1
Size of short : 2
Size of int : 4
Size of long : 8
Size of float : 4
Size of double : 8
Size of long double : 16
Size of bool : 1

sizeof() 不需要用到其他任何库