C/C++编程问题

[meetyu]

#include <fstream>
#include <iomanip>

using namespace std;

int main() {
const int max = 100;
long primes[max] = {2, 3, 5};
int count = 3;
int trial = 5;
bool isprime = true;

do {
trial += 2;
int i = 0;
do {
isprime = trial % *(primes + i) > 0;
} while(++i < count && isprime);
if(isprime)
*(primes + count++) = trial;
} while(count < max);

ofstream outFile("F:\\try\\primes.xml");

for(int i = 0; i < max; ++i){
if(i % 5 == 0)
outFile << endl;
outFile << setw(10) << *(primes + i);
}

return 0;
}

用以上程序将前100素数写入文件,
问题是如何从文件中读取第N个素.同时要求不知道文件中有几个素数的条件下
输入:3
输出:5

[sagegz]

LZ再考虑下如何让首行就开始显示数字.程序有些问题,回来再改.

#include <fstream> 
#include <iomanip>
#include <iostream>

using namespace std; 

int main() { 
	const int max = 100; 
	long primes[max] = {2, 3, 5}; 
	int count = 3; 
	int trial = 5; 
	bool isprime = true;
	do { 
		trial += 2; 
		int i = 0; 
		do{
			isprime = trial % *(primes + i) > 0; 
        } while(++i < count && isprime); 
		if(isprime)
		*(primes + count++) = trial; 
	} while(count < max);
	ofstream outFile("F:\\primes.txt");
	for(int i = 0; i < max; ++i){
		if(i % 5 == 0)
			outFile << endl;
		outFile << setw(10) << *(primes + i);
	}
	ifstream inFile("F:\\primes.txt");
	if(!inFile)
		cerr<<"error!";
	int a[max],i=0;
	for(int b;inFile>>b;){
		a[i] = b;
		++i;
	}	
	cout<<"input the number you want to check: ";
	int number;
	cin>>number;
	cout<<"the result is: ";
	cout<<a[number-1]<<endl;
	return 0; 
} 

[sagegz]

应该跟行没有关系,问题出在for(int b;inFile>>b;)这里,它无法读出最后一行的数据,
如果把max改成105,就能成功读出96-100的数据,否则96-100是读不出正确数据的.
我也不太清楚为什么,等待大牛!

[sunnywyg]

#include <fstream> 
#include <iostream> 
#include <iomanip>

using namespace std; 

int main() 
{ 
	const int max = 100; 
	long primes[max] = {2, 3, 5}; 
	int count = 3; 
	int trial = 5; 
	bool isprime = true; 

	do{
		trial += 2; 
		int i = 0; 
		do {
			isprime = trial % *(primes + i) > 0; 
		}while(++i < count && isprime); 
		if(isprime) 
			*(primes + count++) = trial; 
	} while(count < max); 

	ofstream outFile("d:\\primes.xml", ios::out); 

	for(int i = 0; i < 100; ++i)
	{ 
		if(i % 5 == 0 && i != 0)     //防止第一行是空行
		{
			outFile << endl; 
		}
		outFile << setw(10) << *(primes + i); 
	} 

	cout<<"input the number you want to check: ";
	int number = 0, temp = 0;
	ifstream in("d:\\primes.xml");
	cin>>number;
	while (number-- > 0)
		in >> temp;
	cout << temp;                      //此即为要输出的数
	return 0; 
} 

[邓芳]

哎，我也有一个问题，关于C++的

[genius_tong]

楼上嘛意思？

[九桔猫]

帮顶

[zhaochengzhang]

不懂，帮顶