What is wrong in this code? (Largest and Smallest element in array) - c++

Question

This is my code in C++. When I am taking input {11 10 5 6 7} in the array, Every time it's giving output smallest as 0. But giving correct output to the other inputs.
#include<bits/stdc++.h>
using namespace std;
int main() {
int a[100000];
int large, small;
int n;
cin >> n;
for (int j = 0; j < n; j++) {
cin >> a[j];
}
for (int j = 0; j < n; j++) {
cout << a[j] << " ";
}
large = small = a[0];
for (int i = 1; i <= n; i++) {
if (a[i] < small) {
small = a[i];
}
if (a[i] > large) {
large = a[i];
}
}
cout << "Smallest is " << small << endl;
cout << "Largest is " << large << endl;
}

Answer 1

You have three loops, two of them run while i<n and the third one while i<=n. And then it uses a[n] item. How do you think what the value of a[n] is?

Answer 2

You were asking:
What is wrong in my code
Let me first answer this question and then we will refactor and optimize it.
So, let's list up the findings
#include<bits/stdc++.h> is non-compliant C++ code. It should never be used. It will run only on selected compilers
using namespace std; should not be used. Always use fully qualified names
C-Style arrays, like a[100000] should not be used in C++. Always use dedicated C++ containers like std::array or std::vector or others. In your case, the size of the array is determined at runtime. So, std::vector must be used
the “100000” is a magic number. Why 100000? Why not 500?. And what happens if the user enters 200000 as array size. Then the program will most likely crash
Use always meaningful variable names. Something like “n” will not be understood. The variable “arraySize” would be understood.
Variables shall always be initialized. And only defined, where they are used and not in the beginning of the program
Input should be verified (cin >> n). What will happen, if the user enters ‘x’ and not ‘5’. Remember, you do not initialize variable n.
large and small must be initialized with the smallest / largest value that the relevant data type can hold. Otherwise the result will always be wrong
array indices start with 0 and not with 1. So, your for loop will fail. The result will be wrong. And you used <=n. So, you will access an out of bounds value.
No need to use endl with cout. ‘\n’ will be sufficient
Then, from the design point of view. You do not need an array at all. You can make all checks immediately, directly after reading the next value.
Anyway, let us make the first step of refactoring. And ths adopted to your programming style. We will
still use C-Style arrays and dynamically allocate the memory
even use raw pointers for owned memory and new. Please note. This should not be done!
correct the bugs
use INT_MIN and INT_MAX
use meaningful variable names and comments
Please see the first refactoring step:
#include <iostream>
#include <climits>
int main() {
// Get the array size from the user and validate the input
unsigned int arraySize{};
if ((std::cin >> arraySize) and (arraySize > 0u)) {
// Now, allocate the memory for the array
int* const array = new int[arraySize]();
// Read all values from user into the just allocated array
for (unsigned int index = 0; index < arraySize; ++index) {
// Read value and check, if OK. If not, value will be 0
if (not (std::cin >> array[index])) std::cerr << "\nError: Wrong value\n";
}
// Now we set up the result values, always with the opposite maximum/minimum
int maxValueInArray = INT_MIN;
int minValueInArray = INT_MAX;
// Iterate over all values and check for min and maximum
for (unsigned int index = 0; index < arraySize; ++index) {
// Compare and assign potential new values
if (array[index] < minValueInArray) minValueInArray = array[index];
if (array[index] > maxValueInArray) maxValueInArray = array[index];
}
// Free the allocated memory. We do not need it any longer
delete [] array;
// Show result to user
std::cout << "Smallest is " << minValueInArray << '\n';
std::cout << "Largest is " << maxValueInArray << '\n';
}
else std::cerr << "\nError while reading array size\n\n";
}
So, next, let’s go a little bit more into the direction C++.
We will get rid of raw pointers, new and will use the correct limit values.
#include <iostream>
#include <limits>
#include <memory>
int main() {
// Get the array size from the user and validate the input
unsigned int arraySize{};
if ((std::cin >> arraySize) and (arraySize > 0u)) {
// Now, allocate the memory for the array
std::unique_ptr<int[]> array = std::make_unique<int[]>(arraySize);
// Read all values from user into the just allocated array
for (unsigned int index = 0; index < arraySize; ++index) {
// Read value and check, if OK. If not, value will be 0
if (not (std::cin >> array[index])) std::cerr << "\nError: Wrong value\n";
}
// Now we set up the result values, always with the opposite maximum/minimum
int maxValueInArray = std::numeric_limits<int>::min();
int minValueInArray = std::numeric_limits<int>::max();
// Iterate over all values and check for min and maximum
for (unsigned int index = 0; index < arraySize; ++index) {
// Compare and assign potential new values
if (array[index] < minValueInArray) minValueInArray = array[index];
if (array[index] > maxValueInArray) maxValueInArray = array[index];
}
// Show result to user
std::cout << "Smallest is " << minValueInArray << '\n';
std::cout << "Largest is " << maxValueInArray << '\n';
}
else std::cerr << "\nError while reading array size\n\n";
}
A little bit better. Now we get rid of the whole manual memory allocation and use a std::vector, which is by far better. And we will use range based for loops, which will make our life simpler:
#include <iostream>
#include <limits>
#include <vector>
int main() {
// Get the array size from the user and validate the input
unsigned int arraySize{};
if ((std::cin >> arraySize) and (arraySize > 0u)) {
// Now, allocate the memory for the array
std::vector<int> data(arraySize, 0);
// Read all values from user into the just allocated array
for (int& value : data) {
// Read value and check, if OK. If not, value will be 0
if (not (std::cin >> value)) std::cerr << "\nError: Wrong value\n";
}
// Now we set up the result values, always with the opposite maximum/minimum
int maxValueInArray = std::numeric_limits<int>::min();
int minValueInArray = std::numeric_limits<int>::max();
// Iterate over all values and check for min and maximum
for (const int& value : data) {
// Compare and assign potential new values
if (value < minValueInArray) minValueInArray = value;
if (value > maxValueInArray) maxValueInArray = value;
}
// Show result to user
std::cout << "Smallest is " << minValueInArray << '\n';
std::cout << "Largest is " << maxValueInArray << '\n';
}
else std::cerr << "\nError while reading array size\n\n";
}
And last but not least, we will get of the whole array/vector stuff. It is not needed.
#include <iostream>
#include <limits>
int main() {
// Get the number of values to check from the user and validate the input
unsigned int numberOfValues{};
if ((std::cin >> numberOfValues) and (numberOfValues > 0u)) {
// Now we set up the result values, always with the opposite maximum/minimum
int maxValueInArray = std::numeric_limits<int>::min();
int minValueInArray = std::numeric_limits<int>::max();
// Read all values from user and check them immediately
for (unsigned int i{}; i<numberOfValues; ++i) {
// Read value and check, if OK. If not, value will be 0
int value{};
if (not (std::cin >> value)) std::cerr << "\nError: Wrong value\n";
// Compare and assign potential new values
if (value < minValueInArray) minValueInArray = value;
if (value > maxValueInArray) maxValueInArray = value;
}
// Show result to user
std::cout << "Smallest is " << minValueInArray << '\n';
std::cout << "Largest is " << maxValueInArray << '\n';
}
else std::cerr << "\nError while reading number of values\n\n";
}

Answer 3

On the third loop it will be
for(int i=0;i<n;i++)