One-dimensional arrays in C++ - Step-by-Step Execution

Concept Flow - One-dimensional arrays

Declare array with size

↓

Initialize elements

↓

Access elements by index

↓

Modify elements by index

↓

Use elements in loops or expressions

↓

End of array usage

This flow shows how a one-dimensional array is declared, initialized, accessed, modified, and used in a program.

Execution Sample

C++

int arr[5] = {10, 20, 30, 40, 50};
for (int i = 0; i < 5; i++) {
    arr[i] = arr[i] + 5;
}

This code creates an array of 5 integers, then adds 5 to each element.

Execution Table

Step	i (loop index)	Condition (i < 5)	Action	Array State	Output
1	0	True	arr[0] = 10 + 5	[15, 20, 30, 40, 50]
2	1	True	arr[1] = 20 + 5	[15, 25, 30, 40, 50]
3	2	True	arr[2] = 30 + 5	[15, 25, 35, 40, 50]
4	3	True	arr[3] = 40 + 5	[15, 25, 35, 45, 50]
5	4	True	arr[4] = 50 + 5	[15, 25, 35, 45, 55]
6	5	False	Loop ends	[15, 25, 35, 45, 55]

💡 Loop ends when i reaches 5 and condition i < 5 is false

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
i	undefined	0	1	2	3	4	5
arr	[10, 20, 30, 40, 50]	[15, 20, 30, 40, 50]	[15, 25, 30, 40, 50]	[15, 25, 35, 40, 50]	[15, 25, 35, 45, 50]	[15, 25, 35, 45, 55]	[15, 25, 35, 45, 55]

Key Moments - 3 Insights

Why does the loop stop when i equals 5 and not when i equals 4?

The loop condition is i < 5, so it runs while i is less than 5. When i becomes 5, the condition is false, so the loop stops. This is shown in execution_table row 6.

Why do we start accessing array elements from index 0?

In C++, arrays start at index 0, so the first element is arr[0]. This is why the loop starts with i = 0 and accesses arr[0] first, as seen in execution_table row 1.

What happens if we try to access arr[5] in this example?

Accessing arr[5] is out of bounds because the array size is 5 (indices 0 to 4). This causes undefined behavior and should be avoided. The loop stops before i reaches 5 to prevent this.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of arr after step 3?

A [15, 20, 30, 40, 50]

B [15, 25, 35, 40, 50]

C [10, 20, 30, 40, 50]

D [15, 25, 30, 40, 50]

💡 Hint

Check the 'Array State' column at step 3 in the execution_table.

At which step does the loop condition become false?

A Step 5

B Step 4

C Step 6

D Step 3

💡 Hint

Look at the 'Condition (i < 5)' column in the execution_table to find when it becomes false.

If we change the loop condition to i <= 5, what will happen?

A The loop will run one extra time and access arr[5], causing an error.

B The loop will run the same number of times.

C The loop will not run at all.

D The loop will run fewer times.

💡 Hint

Consider array indices and the loop condition in the execution_table and variable_tracker.

Concept Snapshot

One-dimensional arrays in C++:
- Declared with fixed size: int arr[5];
- Elements accessed by index starting at 0
- Use loops to read or modify elements
- Accessing out-of-bounds index causes errors
- Commonly used for storing sequences of values

Full Transcript

This visual execution trace shows how one-dimensional arrays work in C++. We start by declaring an array of 5 integers with initial values. Then, a loop runs from index 0 to 4, adding 5 to each element. The execution table tracks the loop index, condition, actions, and array state after each step. The variable tracker shows how the loop index and array elements change over time. Key moments clarify why the loop stops at i=5, why indexing starts at 0, and the dangers of out-of-bounds access. The quiz tests understanding of array state at specific steps, loop termination, and effects of changing the loop condition. The snapshot summarizes the main points about one-dimensional arrays in C++.