One-dimensional arrays in C++

Introduction

One-dimensional arrays help you store many values of the same type in a single list. This makes it easy to organize and access data using a simple number called an index.

When you want to keep a list of student scores in a test.

When you need to store daily temperatures for a week.

When you want to hold a sequence of numbers to process them one by one.

When you want to remember the names of players in a game (using an array of strings).

When you want to quickly access data by position without creating many separate variables.

Syntax

C++

class OneDimensionalArray {
public:
    int size;
    int* elements;

    OneDimensionalArray(int array_size) {
        size = array_size;
        elements = new int[size];
    }

    ~OneDimensionalArray() {
        delete[] elements;
    }

    void setElement(int index, int value) {
        if (index >= 0 && index < size) {
            elements[index] = value;
        }
    }

    int getElement(int index) {
        if (index >= 0 && index < size) {
            return elements[index];
        }
        return -1; // Return -1 if index is invalid
    }

    void printArray() {
        for (int i = 0; i < size; i++) {
            std::cout << elements[i] << " ";
        }
        std::cout << std::endl;
    }
};

The array size must be known when creating the array.

Indexing starts at 0, so the first element is at index 0.

Examples

This creates an array of size 5, sets the first and last elements, and prints the array.

C++

OneDimensionalArray arr(5);
arr.setElement(0, 10);
arr.setElement(4, 50);
arr.printArray();

This shows an empty array with size 0. It prints nothing but does not crash.

C++

OneDimensionalArray emptyArray(0);
emptyArray.printArray();

This creates an array with only one element and sets it to 99.

C++

OneDimensionalArray singleElementArray(1);
singleElementArray.setElement(0, 99);
singleElementArray.printArray();

Trying to set elements outside valid indexes does nothing, preventing errors.

C++

OneDimensionalArray arr(3);
arr.setElement(-1, 10); // ignored
arr.setElement(3, 20);  // ignored
arr.printArray();

Sample Program

This program creates a one-dimensional array of size 5, initializes all elements to 0, then sets values at each index. It prints the array before and after setting values. It also shows how to get elements safely, returning -1 for invalid indexes.

C++

#include <iostream>

class OneDimensionalArray {
public:
    int size;
    int* elements;

    OneDimensionalArray(int array_size) {
        size = array_size;
        elements = new int[size];
        for (int i = 0; i < size; i++) {
            elements[i] = 0; // Initialize all elements to 0
        }
    }

    ~OneDimensionalArray() {
        delete[] elements;
    }

    void setElement(int index, int value) {
        if (index >= 0 && index < size) {
            elements[index] = value;
        }
    }

    int getElement(int index) {
        if (index >= 0 && index < size) {
            return elements[index];
        }
        return -1; // Return -1 if index is invalid
    }

    void printArray() {
        for (int i = 0; i < size; i++) {
            std::cout << elements[i] << " ";
        }
        std::cout << std::endl;
    }
};

int main() {
    std::cout << "Creating array of size 5..." << std::endl;
    OneDimensionalArray numbers(5);

    std::cout << "Initial array: ";
    numbers.printArray();

    std::cout << "Setting values..." << std::endl;
    numbers.setElement(0, 10);
    numbers.setElement(1, 20);
    numbers.setElement(2, 30);
    numbers.setElement(3, 40);
    numbers.setElement(4, 50);

    std::cout << "Array after setting values: ";
    numbers.printArray();

    std::cout << "Trying to get element at index 2: ";
    std::cout << numbers.getElement(2) << std::endl;

    std::cout << "Trying to get element at invalid index 10: ";
    std::cout << numbers.getElement(10) << std::endl;

    return 0;
}

Important Notes

Time complexity for accessing or setting an element by index is O(1) because you go directly to the position.

Space complexity is O(n), where n is the size of the array.

Common mistake: Accessing indexes outside the array size causes errors or undefined behavior, so always check index bounds.

Use one-dimensional arrays when you have a fixed number of elements and want fast access by position.

Summary

One-dimensional arrays store multiple values of the same type in a list accessed by index.

Indexes start at 0 and go up to size-1.

They provide fast access and are useful for simple collections of data.

Practice

1. What is the starting index of a one-dimensional array in C++?

easy

A. -1

B. 1

C. 0

D. Depends on the array size

Solution

1. Step 1: Understand array indexing in C++

   Arrays in C++ always start indexing from 0, meaning the first element is at index 0.

2. Step 2: Confirm the index range

   Indexes go from 0 up to size-1, so the first index is always 0 regardless of array size.

3. Final Answer:

   0 -> Option C

4. Quick Check:

   Array indexing starts at 0 [OK]

Hint: Remember: C++ arrays always start at zero index [OK]

Common Mistakes:

• Thinking arrays start at 1
• Assuming negative indexes are valid
• Confusing with other languages

2. Which of the following is the correct way to declare an integer array of size 5 in C++?

easy

A. array<int> arr(5);

B. int arr(5);

C. int arr = new int[5];

D. int arr[5];

Solution

1. Step 1: Recall C++ array declaration syntax

   In C++, a fixed-size array is declared using square brackets with size: int arr[5];

2. Step 2: Check other options for correctness

   int arr(5); uses parentheses which is invalid for arrays. array<int> arr(5); uses incorrect syntax (not standard array). int arr = new int[5]; uses dynamic allocation syntax but is incorrect without pointer.

3. Final Answer:

   int arr[5]; -> Option D

4. Quick Check:

   Fixed-size arrays use square brackets [OK]

Hint: Use square brackets [] to declare fixed-size arrays [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Confusing with vector syntax
• Incorrect dynamic allocation syntax

3. What will be the output of the following code?

int arr[4] = {10, 20, 30, 40};
std::cout << arr[2];

medium

A. 30

B. 20

C. 40

D. Compilation error

Solution

1. Step 1: Identify the array elements and indexes

   The array arr has elements: arr[0]=10, arr[1]=20, arr[2]=30, arr[3]=40.

2. Step 2: Access the element at index 2

   arr[2] is 30, so std::cout will print 30.

3. Final Answer:

   30 -> Option A

4. Quick Check:

   arr[2] = 30 [OK]

Hint: Remember array index starts at 0, so arr[2] is third element [OK]

Common Mistakes:

• Confusing index 2 with 1 or 3
• Expecting output 20 or 40
• Thinking code causes error

4. Identify the error in the following code snippet:

int arr[3] = {1, 2, 3};
for(int i = 0; i <= 3; i++) {
    std::cout << arr[i] << " ";
}

medium

A. Missing semicolon after array declaration

B. Loop runs one time too many, causing out-of-bounds access

C. Syntax error in for loop declaration

D. Array size is incorrect, should be 4

Solution

1. Step 1: Analyze the loop range and array size

   The array has size 3 with valid indexes 0,1,2. The loop runs from i=0 to i=3 inclusive, which means 4 iterations.

2. Step 2: Identify out-of-bounds access

   When i=3, arr[3] is accessed, which is outside the array bounds and causes undefined behavior.

3. Final Answer:

   Loop runs one time too many, causing out-of-bounds access -> Option B

4. Quick Check:

   Loop index must be less than array size [OK]

Hint: Loop index must be less than array size, not less or equal [OK]

Common Mistakes:

• Using <= instead of <
• Assuming array size is 4
• Ignoring out-of-bounds errors

5. Given an integer array arr of size n, which code snippet correctly calculates the sum of all elements?

hard

A. int sum = 0;
for(int i = 0; i < n; i++) sum += arr[i];

B. int sum = 0;
for(int i = 1; i < n; i++) sum += arr[i];

C. int sum = 0;
for(int i = 0; i <= n; i++) sum += arr[i];

D. int sum = arr[0];
for(int i = 1; i < n; i++) sum = arr[i];

Solution

1. Step 1: Understand correct loop bounds for array traversal

   Array indexes go from 0 to n-1, so loop must run i from 0 to less than n.

2. Step 2: Check each option for correctness

   int sum = 0; for(int i = 1; i < n; i++) sum += arr[i]; starts from 1, missing arr[0]. int sum = 0; for(int i = 0; i <= n; i++) sum += arr[i]; uses <= n, causing out-of-bounds access. int sum = 0; for(int i = 0; i < n; i++) sum += arr[i]; correctly sums all elements from 0 to n-1. int sum = arr[0]; for(int i = 1; i < n; i++) sum = arr[i]; overwrites sum instead of adding.

3. Final Answer:

   int sum = 0; for(int i = 0; i < n; i++) sum += arr[i]; -> Option A

4. Quick Check:

   Loop from 0 to n-1 sums all elements [OK]

Hint: Loop from 0 to less than n to cover all elements [OK]

Common Mistakes:

• Starting loop at 1
• Using <= n causing errors
• Overwriting sum instead of adding