如何以简单的方式从 C++ 的循环中删除最后一个逗号? [英] How can I remove the last comma from a loop in C++ in a simple way?

问题描述

这个程序用于打印素数直到给定的输入并用逗号分隔每个素数.

This program is for printing prime numbers till the input given and separating every prime number with a comma.

void main(){

    int N, counter=0, isPrime;

    int k, j;

    cout << "Enter maximum range: ";

    cin >> N;

    for (j=2; j<=N; j++){

        isPrime = 0;
        k = 2;

        while (k<j){

            if (j%k==0){

                isPrime++;
            }
            k++;
        }
        if (isPrime==0){

            if (k==N){
                cout << j;
            }
            else{
                cout << j << ",";
            }
            counter++;
        }
    }
    cout << endl;
    system("pause");
}

它只删除素数输入的最后一个逗号，而不删除任何其他输入.我该如何解决这个问题?

It is only removing the last comma for prime number inputs, not for any other input. How can I fix this?

Input: 23
Output: 2,3,5,7,11,13,17,19,23
Input: 8
Output: 2,3,5,7,
Input: 9
Output: 2,3,5,7,

推荐答案

没必要if then else那么多:

std::string delim = "";
for( auto&& item : vec )
{
   std::cout << delim << item;
   delim = ",";
}

不需要对所有情况进行检查，例如向量是否为空.

No checking is needed for all cases, like the vector is empty or not.

如果在开头接受一个额外的空格，只需将字符串替换为char，那么性能会得到更大的提升.

If you accept an extra space in the beginning, just replace the string to char, and then the performance will be improved even more.

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