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c++ - How do I print an entire vector?

问题描述

I want all items in the vector "listofnums" to print. I tried putting "cout << listofnums[i]" within the for loop thinking it would print each item as it iterated and that didn't work. Putting the cout outside of the loop hasn't worked for me either. 

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

int main(){
    //variables
    int a, b, i = 0; // a & b inputs, i for iterating
    int likedigits = 0; //counts the number of like digits


    //entering number range
    cout << "Enter the first number" << endl;
    cin >> a;
    cout << "Enter the second number" << endl;
    cin >> b;


    //making a vector to contain numbers between a and b
    vector<int> listofnums((b-a)+1); 
    for (i <= (b-a); i++;) {  
        int initialvalue = a;
        listofnums[i] = initialvalue;                                 
        initialvalue++;                                               
    }


    cout << listofnums << endl;
    return 0;
}

标签： c++loopsfor-loopvectorprinting

解决方案

对于初学者来说，for 语句

 for (i <= (b-a); i++;) {

写错了。你的意思是

 for ( ;i <= (b-a); i++) {

在这个（更新的）for循环中

 for ( ;i <= (b-a); i++) {  
    int initialvalue = a;
    listofnums[i] = initialvalue;                                 
    initialvalue++;                                               
}

向量的所有元素都具有值 a，因为变量initialvalue是在每次迭代中定义的。将变量的声明放在 , 循环之外。

   int initialvalue = a;
   for (i <= (b-a); i++;) {  
        listofnums[i] = initialvalue;                                 
        initialvalue++;                                               
    }

要输出向量，您可以使用例如基于范围的 for 循环

for ( const auto &item : listofnums )
{
    std::cout << item << ' ';
}
std::cout << '\n';

这是一个演示程序。

#include <iostream>
#include <tuple>
#include <vector>
#include <algorithm>

int main()
{
    int a = 0, b = 0; 

    std::cout << "Enter the first number: ";
    std::cin >> a;
    std::cout << "Enter the second number: ";
    std::cin >> b;

    std::tie( a, b ) = std::minmax( { a, b } );

    std::vector<int> listofnums( b - a + 1 ); 

    int initialvalue = a;

    for ( auto &item : listofnums ) item = initialvalue++;

    for ( const auto &item : listofnums )
    {
        std::cout << item << ' ';
    }
    std::cout << '\n';

    return 0;
}

它的输出可能如下所示

Enter the first number: 10
Enter the second number: 5
5 6 7 8 9 10

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