Array size and bounds in C - Mini Project: Build & Apply

Array size and bounds

📖 Scenario: You are working on a simple program that stores the ages of a small group of friends. You want to make sure you create an array with the right size and access its elements safely.

🎯 Goal: Create an array to hold exactly 5 ages, set a limit variable for the array size, use a loop to print each age, and display the ages one by one.

📋 What You'll Learn

Create an integer array called ages with exactly 5 elements: 21, 25, 30, 22, 28

Create an integer variable called size and set it to the number of elements in ages

Use a for loop with an index variable i from 0 to size - 1 to access each element in ages

Print each age inside the loop using printf

💡 Why This Matters

🌍 Real World

Arrays are used to store lists of data like ages, scores, or measurements in many programs.

💼 Career

Understanding array size and bounds is essential for writing safe and efficient code in software development.

1

Create the array of ages

Create an integer array called ages with exactly 5 elements: 21, 25, 30, 22, and 28.

C

# Create the array called ages with the 5 given values
// Your code here

Hint

Use the syntax int ages[5] = {value1, value2, value3, value4, value5}; to create the array.

2

Set the size variable

Create an integer variable called size and set it to 5, the number of elements in the ages array.

C

int ages[5] = {21, 25, 30, 22, 28};
// Create the size variable and set it to 5
// Your code here

Hint

Just write int size = 5; to store the array length.

3

Loop through the array

Use a for loop with an index variable i starting at 0 and running while i < size. Inside the loop, access each element of ages using ages[i].

C

int ages[5] = {21, 25, 30, 22, 28};
int size = 5;
// Write a for loop to access each element of ages
// Your code here

Hint

Use for (int i = 0; i < size; i++) and inside the loop use ages[i] to get each age.

4

Print each age

Inside the for loop, use printf to print each age in the format: Age: X where X is the current age from ages[i]. Then run the program to see the output.

C

int ages[5] = {21, 25, 30, 22, 28};
int size = 5;
for (int i = 0; i < size; i++) {
    // Print the current age
    // Your code here
}

Hint

Use printf("Age: %d\n", ages[i]); inside the loop to print each age on its own line.

Practice

1. What is the valid range of indexes for an array declared as int arr[10]; in C?

easy

A. 0 to 9

B. 1 to 10

C. 0 to 10

D. 1 to 9

Solution

1. Step 1: Understand array size declaration

   The array arr is declared with size 10, meaning it has 10 elements.

2. Step 2: Determine valid index range

   In C, array indexing starts at 0, so valid indexes are from 0 up to size-1, which is 9.

3. Final Answer:

   0 to 9 -> Option A

4. Quick Check:

   Array indexes = 0 to size-1 = 0 to 9 [OK]

Hint: Array indexes start at 0 and end at size minus one [OK]

Common Mistakes:

• Assuming array indexes start at 1
• Using size as the last index
• Confusing size with maximum index

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

easy

A. int arr(5);

B. int arr[5];

C. int arr{5};

D. int arr = 5;

Solution

1. Step 1: Recall C array declaration syntax

   In C, arrays are declared using square brackets with the size inside, like int arr[5];.

2. Step 2: Check each option

   int arr[5]; uses correct syntax. Options A and C use parentheses or braces which are invalid for arrays. int arr = 5; assigns an int, not an array.

3. Final Answer:

   int arr[5]; -> Option B

4. Quick Check:

   Array declaration uses square brackets [OK]

Hint: Use square brackets [] to declare array size in C [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Using braces instead of brackets
• Assigning a single value instead of declaring array

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

int arr[3] = {10, 20, 30};
printf("%d", arr[3]);

medium

A. Undefined behavior (may print garbage or crash)

B. 0

C. Compilation error

D. 30

Solution

1. Step 1: Analyze array size and indexing

   The array arr has size 3, valid indexes are 0, 1, 2. Accessing arr[3] is out of bounds.

2. Step 2: Understand consequences of out-of-bounds access

   Accessing outside array bounds in C causes undefined behavior. It may print garbage value, cause crash, or unpredictable output.

3. Final Answer:

   Undefined behavior (may print garbage or crash) -> Option A

4. Quick Check:

   Out-of-bounds access = undefined behavior [OK]

Hint: Accessing index >= size causes undefined behavior [OK]

Common Mistakes:

• Assuming arr[3] prints last element
• Expecting zero instead of garbage
• Thinking compiler catches out-of-bounds

4. Identify the error in the following code snippet:

int arr[4];
for(int i = 0; i <= 4; i++) {
    arr[i] = i * 2;
}

medium

A. Initialization of i is incorrect

B. Array size should be 5 instead of 4

C. Loop condition should be i < 4, not i <= 4

D. Multiplication by 2 is invalid

Solution

1. Step 1: Check loop bounds against array size

   The array size is 4, so valid indexes are 0 to 3. The loop runs while i <= 4, which includes i=4, an invalid index.

2. Step 2: Correct the loop condition

   Changing the loop condition to i < 4 ensures indexes 0 to 3 are used, avoiding out-of-bounds access.

3. Final Answer:

   Loop condition should be i < 4, not i <= 4 -> Option C

4. Quick Check:

   Loop index must be less than array size [OK]

Hint: Use < not <= for loop index to avoid out-of-bounds [OK]

Common Mistakes:

• Using <= instead of < in loop condition
• Assuming array size includes index equal to size
• Ignoring off-by-one errors

5. Given the array declaration int nums[5] = {1, 2, 3, 4, 5};, which code snippet correctly sums all elements without causing out-of-bounds errors?

hard

A. for(int i = 0; i < 6; i++) sum += nums[i];

B. for(int i = 1; i < 5; i++) sum += nums[i];

C. for(int i = 0; i <= 5; i++) sum += nums[i];

D. for(int i = 0; i < 5; i++) sum += nums[i];

Solution

1. Step 1: Understand array size and valid indexes

   The array nums has size 5, so valid indexes are 0 to 4.

2. Step 2: Evaluate each loop condition

   for(int i = 0; i <= 5; i++) sum += nums[i]; uses i <= 5, which accesses nums[5] (out-of-bounds). for(int i = 1; i < 5; i++) sum += nums[i]; starts at 1, missing nums[0]. for(int i = 0; i < 5; i++) sum += nums[i]; uses i < 5, correctly iterating 0 to 4. for(int i = 0; i < 6; i++) sum += nums[i]; uses i < 6, accessing nums[5] (out-of-bounds).

3. Final Answer:

   for(int i = 0; i < 5; i++) sum += nums[i]; -> Option D

4. Quick Check:

   Loop from 0 to size-1 to avoid errors [OK]

Hint: Loop from 0 to less than array size for safe access [OK]

Common Mistakes:

• Using <= size causing out-of-bounds
• Starting loop at 1 missing first element
• Looping beyond array size