Finding max value in a array

Question

I'm doing a program that finds the max value in a array. I done it but I found a strange bug.

#include<iostream>

using namespace std;

int main() {
    int n; //input number of elements in 
    cin >> n;
    int arr[n];
    for (int i = 0; i < n; i++) {
        cin >> arr[i]; //input array's elements
    } int max_value = arr[0];
    for (int i = 1; i <= n; i++) {
        if (arr[i] > max_value) {
            max_value = arr[i];
        }
    } cout << max_value;
    return 0;
}

When I put 5 as first line for the number of elements and 2, 7, 6, 8, 9 as the elements of the array. It returns 16 instead of 9. Please help

Answer 1

In Arrays the first index starts with 0 and ends in n - 1 assuming the array is of length n

so when looping from i = 1 to i <= n . n is now larger than n - 1 . the solution would be to start from 0 and end at i < n hence.

#include<iostream>

using namespace std;

int main() {
    int n; //input number of elements in 
    cin >> n;
    int arr[n];
    for (int i = 0; i < n; i++) {
        cin >> arr[i]; //input array's elements
    } int max_value = arr[0];
    for (int i = 0; i < n; i++) {
        if (arr[i] > max_value) {
            max_value = arr[i];
        }
    }
    cout << max_value;
    return 0;
}

you could also use the std::max function like so:

for(int i = 0; i < n; i ++) {
   max_value = max(max_value, arr[i]);
}

Answer 2

in your second for do this

for (int i = 1; i < n; i++) {
    if (arr[i] > max_value) {
        max_value = arr[i];
    }

delete '=' from i <= n because i is index which start from 0

and instead of this

int arr[n];

do this

int *arr = new int[n];

Answer 3

The other posts already pointed out problem in your code.

You should be aware of that int arr[n]; is not permitted in standard C++.
[GCC and CLANG compiler support it in C++ as an extension]

An alternative is to allocate memory dynamically:

    int *arr = new int[n];

and to find maximum value you can use std::max_element :

    int max_value = *(std::max_element(arr, arr + n));

Instead of dynamic array, its better to use vector STL (make yourself familiar with Containers Library ). You can do:

    std::vector <int> arr;

    for (int i = 0; i < n; i++) {
        int input;
        std::cin >> input;
        arr.push_back(input);
    } 

    int max_value = *std::max_element(arr.begin(), arr.end());
    std::cout << "Max element is :" << max_value << std::endl;