C++学习笔记

文件读写操作

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
void main(int argc, char* argv[])
{
	ifstream in("C:\\Users\\Administrator\\Desktop\\C++.txt",ifstream::out);
	ofstream out("C:\\Users\\Administrator\\Desktop\\CC.txt",ifstream::app);
	if(!in)
	{
		cout<<"Cannot open input file!"<<endl;
	}

	string str;
	while(getline(in,str))
	{
		out.write(str.c_str(),str.size());
		out.write("\n",1);
	}
}

 atoi和itoa实现：

#include <iostream>

using namespace std;
int atoi(char* ch);
char* itoa(int n,char* ch);
char* reverse(char* ch);

void main(int argc, char* argv[])
{
	char* ch = "123579";
	int a = atoi(ch);
	cout<<a<<endl;

	int n = 752456;
	char cc[10];
	char* c = itoa(n,cc);
	cout<<c<<endl;
}

int atoi(char* ch)
{
	int i = 0;
	int num = 0;
	while (ch[i] != '\0')
	{
		num = num * 10 + ch[i]- '0';
		i++;
	}
	return num;
}

char* itoa(int n,char* ch)
{
	int i = 0;
	while(n)
	{
		ch[i++] = n % 10 + '0';
		n = n / 10;
	}
	ch[i]='\0';
	return reverse(ch);
}

char* reverse(char* ch)
{
	int size = 0;
	while(ch[size]!='\0')
	{
		size++;
	}

	char temp;
	for(int i = 0, j = size - 1; i < j; i++,j--)
	{
		temp = ch[i];
		ch[i] = ch[j];
		ch[j] = temp;
	}
	return ch;
}

读取一组整数，判断某个值的个数

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

void main(int argc, char* argv[])
{
	int num;
	vector<int> nums;
	while(cin>>num)
	{
		if(num==-1) break;
		nums.push_back(num);
	}
	
	int number = 5;
	int times = 0;
	vector<int>::const_iterator result = find(nums.cbegin(),nums.cend(),number);
	while(result != nums.cend())
	{
		times++;
		result++;
		result = find(result,nums.cend(),number);
	}
	cout<<"Total Times of 5 is: "<<times<<endl;
}