C++基礎編程DAY18

45、寫一函數，在一數組裏查找某個值

//寫一函數，在一數組裏查找某個值
#include<iostream>
#include<stdlib.h>

using namespace std;

int Search(int a[], int n, int key)
{
	int i;
	for(i=0; i<n; i++)
	{
		if(a[i]==key)
		{
			//cout << "a[" << i << "]=" << a[i] << endl;
			return i;
		}
		//else return -1;
	}
	return -1;//key不在a[]中，返回-1，表示該函數失敗
}

int main()
{
	int a[10] = {0,1,2,3,4,5,6,7,8,9};
	int key;
	cin >> key;
	cout << Search(a,10,key);
	system("pause");
	return 0;
}

46、編一程序，求兩個矩陣的乘積

#include <iostream>
#include <stdlib.h>

using namespace std;

int main ()
{
	int m,n,a,b,i,j,k;
	int **a1;
	int **b1;
	int **c1;
	
	cout<<"輸入第一個矩陣的行數與列數:";
	cin>>m>>n;
	cout <<"輸入第二個矩陣的行數與列數:";
	cin>>a>>b;
    if(n != a)
	{
		cout<<"維數不同無法相乘"<<endl;
		exit(-1);
	}

	//動態內存分配
	a1 = new int *[m]; 
    for (i=0; i<m; i++)
		if ((a1[i] = new int [n])==NULL)
			exit (0);
	
	b1 = new int * [a]; 
	for (i = 0;i<a;i++)
		if ((b1[i] = new int [b])==NULL)
			exit (0);
	
	c1 = new int * [m];
	for (i=0; i<m; i++)
		if ((c1[i] = new int [b])==NULL)
			exit (0);

	//創建矩陣a1
	cout<<"輸入第一個矩陣的元素:";
	for (i=0; i<m; i++)
	{
		for(j=0; j<n; j++)
			cin>>a1[i][j];
	}
	//創建矩陣b1
		cout<<"輸入第二個矩陣的元素:";
	for (i=0; i<a; i++)
	{
		for (j=0; j<b; j++) 
			cin>>b1[i][j];
	}
	//將c1矩陣所有元素賦值爲0
    for (i=0; i<m; i++)
		for (j=0; j<b; j++)
			c1[i][j] = 0;
	//計算c1
	for (i=0; i<m; i++)
		for(j=0; j<b; j++)
			for (k=0; k<n; k++)
				c1[i][j] += a1[i][k]*b1[k][j];

	//輸出c1
	cout<<"輸出結果爲"<<endl;
	for (i=0; i<m; i++)
	{
		k = 0;
		for (j=0; j<b; j++)
		{
			cout<<c1[i][j];
			k = k+1;
			if (k==b)
				cout<<endl;
			else cout<<"\t";
		}
	}

	//釋放內存空間
	for (i=0; i<m; i++)
		delete[]a1[i];
	delete []a1;
	for (i=0; i<a; i++)
		delete[]b1[i];
	delete []b1;
	for (i = 0;i<m;i++)
		delete[]c1[i];
	delete []c1;

	system("pause");
	return 0;
}

參考代碼：C++編程求兩個矩陣的乘積

47、計算某日是某年的第幾天

//計算某日是某年的第幾天
#include<iostream>
#include<stdlib.h>

using namespace std;

/*判斷是否爲閏年*/
bool isLeapYear(int n)
{
	if(n%4 == 0) return true;
	return false;
}

/*計算天數*/
 int count_days(int year, int mon, int date)
 {
	 int s=0;
	 switch(mon-1)
	 {
	 //case 12: s+=31;
	 case 11: s+= 30;
	 case 10: s+= 31;
	 case 9: s += 30;
	 case 8: s += 31;
	 case 7: s += 31;
	 case 6: s += 30;
	 case 5: s += 31;
	 case 4: s += 30;
	 case 3: s += 31;
	 case 2: s += 28;
	 case 1: s += 31;
	 //case 0: s += 0;
	 default:;
	 }
	 if(isLeapYear(year)) s++;
	 return s = s + date;
 }

 int main()
 {
	 int year, mon, date;
	 cout << "請輸入年月日：";
	 cin >> year >> mon >> date;
	 cout << year << "年" << mon << "月" << date << "日是" << year << "的第";
	 cout <<count_days(year, mon, date) << "天" << endl;
	 system("pause");
	 return 0;
 }

48、編寫一個幫助小學生學習加法的程序，隨機產生2個數，讓學生輸入答案

//編寫一個幫助小學生學習加法的程序，隨機產生2個數，讓學生輸入答案。

#include<iostream>
#include<stdlib.h>
#include<time.h>

using namespace std;

/* 獲得隨機數1-100 */
int get_randomNO()
{
	//int a;
	//a = rand()%6 + 1;
	//cout << rand() << endl;
	return rand()%100 + 1;
}

int main()
{
	int a, b, c;
	//unsigned seed;
	//seed = time(0);
	//srand(seed);
	srand(time(0));
	for(int i=0; i<5; i++)//練習次數
	{
		a = get_randomNO();
		b = get_randomNO();
		cout << a << " + " << b << " = ";
		cin >> c;
		if(c == a+b)
			cout << "回答正確" << endl;
		else
			cout << "回答錯誤，正確答案是" << a+b << endl;
	}
	system("pause");
	return 0;
}

49、從52個數裏選13個數

//從52個數裏選13個數

#include<iostream>
#include<stdlib.h>
#include<time.h>

using namespace std;

int main()
{
	int a[53]={0}, b[13]={0}, t, i, j;
	for(int i=1; i<=52; i++)
		a[i] = i;
	srand(time(0));
	/*獲得13個1-52之間不重複的數*/
	for(int j=1; j<=13; j++)
	{
		a[j] = rand()%52 + 1;
		for(int k=0; k<j; k++)
			if(a[j] == a[k])//如果與前面的數重複，執行j-1，重搖
			{
				j--;
				break;
			}
	}
	/*排序*/
	for(i=1; i<=13; i++)
		for(j=1; j<=13-i; j++)
		{
			if(a[j]>a[j+1])
			{
				t = a[j];
				a[j] = a[j+1];
				a[j+1] = t;
			}
		}
	for(i=1; i<=13; i++)
		cout << a[i] << " ";
	system("pause");
	return 0;
}

題目來源：50道C/C++編程練習題及答案

總結

1、題45中return -1;作爲key不在數組中的返回標誌；參考：C++函數返回值介紹（含return 0 與 return 1 與 return -1介紹
2、C++二維數組指針