Array access
- C++ course
- Beginner
- Lesson 54/116
- 4 min
Learn to access and modify array elements by index.
Array access
To access array elements you write the index inside square brackets. nums[0] gives the first element, nums[2] the third. Because indices start at zero, nums[i] actually represents the (i+1)th element.
The same syntax lets you change an element: nums[1] = 99; sets the second element to 99. Using an index beyond the array size (such as nums[10] on a five-element array) causes undefined behavior, so keep the index under control.
Modifying arrays
You can change array contents by assigning to its elements. Writing nums[1] = 99; changes only that element; others stay the same. This lets you update the array from a single point.
You can rewrite all elements by assigning in a loop. For example for (int i = 0; i < 5; i++) nums[i] = 0; zeroes every element. Because the array size is fixed, memory management is automatic; you do not need new or delete.
Practice Change the second element and print it
The nums array is set to {10, 20, 30, 40, 50}. Change the second element with nums[1] = 99; and print it with std::cout << nums[1];. The output must be 99.
Starter code
#include <iostream>
int main() {
int nums[5] = {10, 20, 30, 40, 50};
// Change the second element to 99 and print it
return 0;
}Sample solution
#include <iostream>
int main() {
int nums[5] = {10, 20, 30, 40, 50};
nums[1] = 99;
std::cout << nums[1] << std::endl;
return 0;
}Expected output
99
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Write the third element
int nums[5] = {10, 20, 30, 40, 50};
std::cout << ____;int nums[5] = {10, 20, 30, 40, 50};
std::cout << nums[2];Explanation: nums[2] gives the third element, 30.
2 Match each access pattern to its meaning
| Term | Meaning |
|---|---|
nums[0] |
First element |
nums[1] |
Second element |
nums[4] |
Last element (5 elements) |
nums[i] |
i-th index |
3 What does nums[3] = 99; do?
int nums[5] = {10,20,30,40,50};
nums[3] = 99;- Reads the third element
- Divides the array by 3
- Sets the fourth element to 99 Correct answer
- Sets the total to 99
Explanation: nums[3] = 99; sets the fourth element to 99 (index 3).