Problem: i cant find the minimum, it's always zero!why?

#include <iostream>
using namespace std;
int main(){     // input n numbers & show max & min

int n, x, max = x, min = x;
cin>>n;
    for(int i = 1; i <= n; i  ){
    cin>>x;
        if (x>max){
            max = x;
        }else if (x<min){
            min = x;
        }
    }
cout<<"max: "<<max<<endl<<"min: "<<min; 
    return 0;
}

I try to give n inputs and find the maximum & minimum between them with my codes.

CodePudding user response：

You need to choose an initial value for min and max. You choose x but x is not initialized, it has an indeterminate value. Using x to initialize min and max leads to undefined behavior.

You can use the first element as initial value for min and max. However, rather than fixing your mistake you can avoid it completely: Let someone else find min and max for you.

There is std::minmax_element that given two iterators to being and end of a range returns a pair of iterator to the minimum element and iterator to maximum element. The iterators you pass to std::minmax_element do not have to be iterators to a container, they can be std::istream_iterators that read from std::cin on the fly.

#include <iostream>
#include <algorithm>
#include <iterator>

int main() {   
    auto res = std::minmax_element(std::istream_iterator<int>(std::cin),
                     std::istream_iterator<int>());
    std::cout << *(res.first) << " " << *(res.second) ;
}

Live Demo

It takes a bit to understand the code. I hope the links above help with that. But once you know what the code does it is as simple as it can get. There is almost no possibility to get something wrong. Well of course there are some, but for example it is just not possible to have wrong initial values for min or max in this code.

CodePudding user response：

Using std::vector, std::sort/std::minmax_element your code would look like this (also no index based loops):

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

int main()
{
    std::size_t number_of_numbers;

    std::cout << "How many numbers : ";
    std::cin >> number_of_numbers;

    // TODO check in put != 0 or 1;

    std::vector<int> values(number_of_numbers);

    // range based for will not go out of bounds
    for (auto& value : values) // reference to value in array so it can be changed
    {
        std::cout << "Input number : ";
        std::cin >> value;
    }

    // using min element
    auto pair_t = std::minmax_element(values.begin(), values.end());
    auto min = *pair_t.first;
    auto max = *pair_t.second;
    std::cout << "min element = " << min << "\n";
    std::cout << "max element = " << max << "\n";

    // using sort
    std::sort(values.begin(), values.end());
    std::cout << "first element in sorted vector : " << values.front() << "\n";
    std::cout << "last element in sorted vector : " << values.back() << "\n";
    return 0;
}

CodePudding user response：

correction:

#include <iostream>
using namespace std;
int main(){     // input n numbers & show max & min

int n, x, f;
cin>>n;
cin>>x;
f = x;
int max = f, min = f;
    for(int i = 1; i < n; i  ){
    cin>>x;
        if (x>max){
            max = x;
        }else if (x<min){
            min = x;
        }
    }
cout<<"max: "<<max<<endl<<"min: "<<min; 
    return 0;
}