来自'std :: ios_base＆amp;的转换无效（*）（std :: ios_base＆amp;）'到'int'[-fpermissive]

Question

我已经实现了查找max和min的函数。但我得到以下错误代码：    [错误]来自'std :: ios_base＆amp;的无效转换（*）（std :: ios_base＆amp;）'到'int'[-fpermissive]

#include<iostream>
    using namespace std;
    int a[1000], n, maxDiff, maxValue, minValue;
    void nhap() {
        int i, n;
        cout << "Nhap n: ";
        cin >> n;
        for ( int i =1; i <= n; i ++) {
            cout << "Nhap vao mang thu i: " << i << endl;
            cin >> a[i];
        } 
    }
    void findmaxdiff(int left, int right, int maxDiff, int& maxValue, int& minValue) {
        int mid;
        int maxD1, maxV1, minV1;
        int maxD2, maxV2, minV2;
        if(left==right) {
            maxDiff = 0;
            maxValue = a[right];
            minValue = a[right];
        }
        else {
            mid = (left +right) / 2;
            findmaxdiff(left, mid, maxD1, maxV1, minV1);
            findmaxdiff(mid+1, right, maxD2, maxV2, minV2);
            maxDiff = maxV2 - minV1;
            if(maxDiff< maxD1) maxDiff = maxD1;
            if(maxDiff< maxD2) maxDiff = maxD2;
            if(maxV1> maxV2){
                maxValue= maxV1;
            }
            else {
                maxValue = maxV2;
            }
            if(minV1< minV2) {
                minValue = minV1;
            }
            else {
                minValue= minV2;
            }
        }
    }
    int main() {
        nhap();
        findmaxdiff(left, n, maxDiff, maxValue, minValue);
        cout << maxDiff;
    }

Answer 1

缺少变量#include "iostream" #include <string> using namespace std; class Base { public: int value; string name; Base(int _value, string _name) : value(_value),name(_name) { } virtual void print() { cout << "name is " << name << " value is " << value << endl; } }; class Child : public Base{ public: int value2; Child(int _value, string _name, int _value2): Base(_value,_name), value2(_value2) { } virtual void print() { cout << "name is " << name << " value is " << value << " value2 is " << value2 << endl; } }; int main() { Base base = Base(10,"base"); Child child = Child(11,"child",22); Base* base_array[2]; base_array[0] = &base; base_array[1] = &child; base_array[0]->print(); base_array[1]->print(); return 0; } 定义。

不要left将std命名空间扩展到全局命名空间中，您将避免此类错误。您忘记声明变量using namespace std;，并且已应用名称空间left中的std::ios_base& left( std::ios_base& str );函数。

Why is using namespace std considered bad practice?