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C++ One-Dimensional Arrays — Syntax & Examples


Beginner-friendly guide to C++ one-dimensional arrays: declaration, initialization, indexing, accessing elements, loops, and practical examples.

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🔹 What is an Array?

An array is a collection of multiple values of the same data type stored in continuous memory locations under one variable name.

👉 Instead of creating many variables, we use an array.

Example:

int marks[5];

This stores 5 integer values.

🔹 One-Dimensional Array

A one-dimensional array stores data in a single line (row).

📌 Syntax:

data_type array_name[size];

🔹 Declaring a One-Dimensional Array

Declaration means reserving memory for the array.

Example:

int numbers[5];

📌 This creates an array named numbers that can store 5 integers.

array structure

🔹 Array Initialization

Initialization means assigning values to the array.

Method 1: Initialize at Declaration

int numbers[5] = {10, 20, 30, 40, 50};

Method 2: Let Compiler Count Size

int numbers[] = {5, 10, 15, 20};

Method 3: Initialize One by One

int numbers[3];
numbers[0] = 10;
numbers[1] = 20;
numbers[2] = 30;

🔹 Index Number (Very Important)

  • Array index starts from 0
  • Last index = size - 1
Index Value
0 First element
1 Second element
2 Third element

🔹 Accessing Individual Elements

We use index number to access elements.

Example:

int numbers[5] = {10, 20, 30, 40, 50};

cout << numbers[0]; // Output: 10
cout << numbers[3]; // Output: 40

📌 Example: Assigning Value to Individual Array Elements

#include <iostream>
using namespace std;

int main() {
    int numbers[5];   // Array declaration

    // Assigning values to individual elements
    numbers[0] = 10;
    numbers[1] = 20;
    numbers[2] = 30;
    numbers[3] = 40;
    numbers[4] = 50;

    // Displaying values
    cout << numbers[0] << endl;
    cout << numbers[1] << endl;
    cout << numbers[2] << endl;
    cout << numbers[3] << endl;
    cout << numbers[4] << endl;

    return 0;
}

🔍 Explanation

  • int numbers[5]; → creates an array of size 5
  • numbers[0] = 10; → assigns 10 to the first element
  • numbers[1] = 20; → assigns 20 to the second element
  • Index starts from 0, not 1
  • Each element is accessed using array name + index

📘 Memory View (Simple)

Index Value
0 10
1 20
2 30
3 40
4 50

🔹 Accessing Array Elements Using for Loop

The for loop is best for accessing array elements.

Example:

#include <iostream>
using namespace std;

int main() {
    int numbers[5] = {10, 20, 30, 40, 50};

    for(int i = 0; i < 5; i++) {
        cout << numbers[i] << endl;
    }
    return 0;
}

📌 i represents the index number.

🔹 Example 1: Print Student Marks

Problem:

Store and display marks of 5 students.

#include <iostream>
using namespace std;

int main() {
    int marks[5] = {78, 85, 90, 66, 88};

    for(int i = 0; i < 5; i++) {
        cout << "Student " << i+1 << " Marks: " << marks[i] << endl;
    }

    return 0;
}

🔹 Example 2: Sum of Array Elements

Problem:

Find sum of array values.

#include <iostream>
using namespace std;

int main() {
    int numbers[5] = {10, 20, 30, 40, 50};
    int sum = 0;

    for(int i = 0; i < 5; i++) {
        sum = sum + numbers[i];
    }

    cout << "Sum = " << sum;

    return 0;
}

🔹 Example 3: Store and Display Marks of Students

#include <iostream>
using namespace std;

int main() {
    int marks[5];   // Declare an array of size 5

    // Taking input
    cout << "Enter marks of 5 students:" << endl;
    for(int i = 0; i < 5; i++) {
        cin >> marks[i];
    }

    // Displaying output
    cout << "Marks of students are:" << endl;
    for(int i = 0; i < 5; i++) {
        cout << marks[i] << endl;
    }

    return 0;
}

🔍 Explanation (Very Simple)

1️⃣ Array Declaration

int marks[5];
  • int → data type
  • marks → array name
  • 5 → size (number of elements)

2️⃣ Taking Input Using for Loop

for(int i = 0; i < 5; i++) {
    cin >> marks[i];
}
  • i is the index
  • Index starts from 0
  • Values are stored one by one

3️⃣ Displaying Array Values

for(int i = 0; i < 5; i++) {
    cout << marks[i] << endl;
}
  • Prints each element of the array

📊 How Data is Stored

Index Value
0 marks of student 1
1 marks of student 2
2 marks of student 3
3 marks of student 4
4 marks of student 5

🔹 Example 4: Find the Sum of Numbers Using an Array

💡 Problem Statement

Store 5 numbers in an array and calculate their sum.

✅ Program:

#include <iostream>
using namespace std;

int main() {
    int numbers[5];
    int sum = 0;

    // Taking input
    cout << "Enter 5 numbers:" << endl;
    for(int i = 0; i < 5; i++) {
        cin >> numbers[i];
    }

    // Calculating sum
    for(int i = 0; i < 5; i++) {
        sum = sum + numbers[i];
    }

    // Displaying result
    cout << "Sum of numbers = " << sum << endl;

    return 0;
}

🔍 Explanation (Simple Words)

1️⃣ Array Declaration

int numbers[5];

Creates an array to store 5 integers.

2️⃣ Input Using Loop

  • Values stored in:
numbers[0] to numbers[4]

3️⃣ Sum Calculation

sum = sum + numbers[i];

Adds each element to sum.

📊 Example Input / Output

Input:

10 20 30 40 50

Output:

Sum of numbers = 150

📘 Related Topics