代码块中变量的全球化

Question

我在使用在代码中的第一个if语句（if（choice == 1））中创建的数组/矩阵时遇到问题。我想编辑数组（当我提到if（choice == 2）时，但是在第一个“if”代码块中创建的数组是本地化的。我怎样才能解决这个问题？

#include "pch.h"
#include <iostream>
#include <vector>

int main()
{
        if (choice == 1)
        {
            std::cout << "Choose a letter from A to C, where A = 1" << std::endl;
            short matNamechoice;
            std::cin >> matNamechoice;

            if (matNamechoice == 1)
            {
                bool matAlive = true;
                std::vector<int> matrixA(0);
                std::cout << "How many elements would you like to add to Matrix" << matNamechoice << "?" << std::endl;
                short matAelements;
                std::cin >> matAelements;
                std::cout << "For the " << matAelements << "elements that you have created, please choose \
                    each element value: " << std::endl;
                for (int n = 0; n < matAelements; ++n)
                {
                    std::cout << "ELEMENT NO " << n << ":" << std::endl;
                    int elementValue = 0;
                    std::cin >> elementValue;
                    matrixA.push_back(elementValue);
                }
                std::cout << matAelements << " elements have been appended to matrixA." << std::endl;
            }


            if (matNamechoice == 2)
            {

                bool matBLive = true;
                std::vector<int> matrixB(0);
                std::cout << "How many elements would you like to add to Matrix " << matNamechoice << "?" << std::endl;
                short matBelements;
                std::cin >> matBelements;
                std::cout << "For the " << matBelements << "elements that you have created, please choose \
                        each element value: " << std::endl;
                for (int n = 0; n < matBelements; ++n)
                {
                    std::cout << "ELEMENT NO " << n << ":" << std::endl;
                    int elementValue = 0;
                    std::cin >> elementValue;
                    matrixB.push_back(elementValue);
                }
                std::cout << matBelements << " elements have been appended to matrixB." << std::endl;
            }


            if (matNamechoice == 3)
            {

                bool matCLive = true;
                std::vector<int> matrixC(0);
                std::cout << "How many elements would you like to add to Matrix" << matNamechoice << "?" << std::endl;
                short matCelements;
                std::cin >> matCelements;
                std::cout << "For the " << matCelements << "elements that you have created, please choose \
                each element value: " << std::endl;
                for (int n = 0; n < matCelements; ++n)
                {
                    std::cout << "ELEMENT NO " << n << ":" << std::endl;
                    int elementValue = 0;
                    std::cin >> elementValue;
                    matrixC.push_back(elementValue);
                }
                std::cout << matCelements << " elements have been appended to matrixC. \n \n" << std::endl;
            }
        }

        if (choice == 2 && (matAlive == true))
            std::cout << "LOADING MATRICIES..." << std::endl;
            for (int n = 10; n <= 100; n += 10)
            {
                std::cout << n << "%" << std::endl;

            }
            std::cout << "MATRIX DATA LOAD SUCCESSFUL..." << std::endl;
            std::cout << "Enter 1 to edit a Matrix. Enter 2 to print a Matrix. Enter 3 to clear a Matrix." << std::endl;
            short userChoice = 0;
            std::cin >> userChoice;
    }

    int x = 0;

    if (x < 100)
    {
        int y = 1;
    }

    return 0;
}

Answer 1

将变量移到内部块之外：

bool matAlive = false;
std::vector<int> matrixA(0);

if (choice == 1) {
    if (matNamechoice == 1) {
        matAlive = true;
        // ...
    }
}
// ...
if (choice == 2 && (matAlive == true)) {
    // ...
}