Array traversal in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does array traversal mean in C programming?

Array traversal means visiting each element of an array one by one, usually using a loop, to read or modify its values.

beginner

Which loop is commonly used for array traversal in C?

The for loop is commonly used because it allows easy control of the index from 0 to the array size minus one.

beginner

What is the starting index of an array in C?

The starting index of an array in C is 0, meaning the first element is accessed with index 0.

beginner

Show a simple C code snippet to print all elements of an integer array named arr of size n.

for (int i = 0; i < n; i++) { printf("%d\n", arr[i]); }

beginner

Why is it important to use the correct array size when traversing an array?

Using the correct size prevents accessing memory outside the array, which can cause errors or crashes.

What is the first index used when traversing an array in C?

A -1

B 1

C 0

D Array size

Arrays in C start at index 0, so traversal begins at 0.

Which loop is best suited for traversing an array when the size is known?

A for loop

B do-while loop

C while loop

D switch statement

The for loop is ideal for known sizes because it controls the index easily.

What happens if you traverse beyond the array size in C?

A Undefined behavior, possible crash or wrong data

B Array automatically resizes

C Compiler error

D Program safely ignores extra elements

Accessing outside array bounds causes undefined behavior and can crash the program.

How do you access the third element of an array named arr?

A arr[3]

B arr[2]

C arr[1]

D arr[0]

Since indexing starts at 0, the third element is at index 2.

Which of these is a correct way to traverse an array of size n?

A for (int i = n; i > 0; i--)

B for (int i = 1; i <= n; i++)

C for (int i = 0; i <= n; i++)

D for (int i = 0; i < n; i++)

Looping from 0 to less than n covers all valid indices.

Explain how to traverse an array in C and why the starting index is important.

Think about how arrays are indexed and how loops help visit each element.

Describe what could happen if you try to access an array element outside its size during traversal.

Consider what happens when you read memory not allocated for the array.

Practice

1. What does array traversal mean in C programming?

easy

A. Adding elements to the array

B. Deleting elements from the array

C. Visiting each element of the array one by one

D. Sorting the array elements

Solution

1. Step 1: Understand the term 'array traversal'

   Array traversal means going through each element in the array in order.

2. Step 2: Match the definition with options

   Only Visiting each element of the array one by one describes visiting each element one by one, which is the correct meaning.

3. Final Answer:

   Visiting each element of the array one by one -> Option C

4. Quick Check:

   Array traversal = visiting elements [OK]

Hint: Traversal means visiting all elements one by one [OK]

Common Mistakes:

• Confusing traversal with adding or deleting elements
• Thinking traversal means sorting
• Assuming traversal skips elements

2. Which of the following is the correct syntax to traverse an array arr of size n in C?

easy

A. for(int i = 0; i < n; i++)

B. for(int i = 1; i <= n; i++)

C. for(int i = 1; i < n; i++)

D. for(int i = 0; i <= n; i++)

Solution

1. Step 1: Understand array indexing in C

   Arrays start at index 0 and go up to n-1 for size n.

2. Step 2: Check loop conditions

   The loop must start at 0 and run while i is less than n (not equal), so for(int i = 0; i < n; i++) is correct.

3. Final Answer:

   for(int i = 0; i < n; i++) -> Option A

4. Quick Check:

   Loop from 0 to n-1 = correct traversal [OK]

Hint: Loop from 0 to less than n for array traversal [OK]

Common Mistakes:

• Using <= n causes out-of-bounds error
• Starting loop at 1 misses first element
• Using wrong loop condition

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

int arr[] = {5, 10, 15};
for(int i = 0; i < 3; i++) {
    printf("%d ", arr[i]);
}

medium

A. 5 10 15 0

B. 15 10 5

C. 10 15 5

D. 5 10 15

Solution

1. Step 1: Understand the array elements

   The array contains 5, 10, and 15 in order at indices 0, 1, and 2.

2. Step 2: Trace the loop output

   The loop prints elements from index 0 to 2 in order, so output is "5 10 15 "

3. Final Answer:

   5 10 15 -> Option D

4. Quick Check:

   Print elements in order = 5 10 15 [OK]

Hint: Prints elements in order from index 0 to n-1 [OK]

Common Mistakes:

• Reversing order of output
• Printing extra zero
• Starting loop at wrong index

4. Identify the error in the following code snippet for traversing an array arr of size 5:

for(int i = 0; i <= 5; i++) {
    printf("%d ", arr[i]);
}

medium

A. Loop condition should be i < 5 to avoid out-of-bounds access

B. Loop variable should start from 1 instead of 0

C. Array size should be 6 instead of 5

D. No error, code is correct

Solution

1. Step 1: Check loop condition

   The loop runs while i <= 5, so i goes from 0 to 5 inclusive (6 iterations).

2. Step 2: Analyze array indexing

   Array indices go from 0 to 4 for size 5. Accessing arr[5] is out-of-bounds and causes error.

3. Final Answer:

   Loop condition should be i < 5 to avoid out-of-bounds access -> Option A

4. Quick Check:

   Use i < size to avoid errors [OK]

Hint: Use i < size, not i <= size, to avoid out-of-bounds [OK]

Common Mistakes:

• Using <= instead of <
• Starting loop at 1
• Ignoring array size limits

5. Given an integer array arr of size n, write a code snippet to find the sum of all elements using array traversal. Which of the following is correct?

hard

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

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

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

D. int sum = 0;
for(int i = n - 1; i >= 0; i--) {
sum += arr[i];
}

Solution

1. Step 1: Understand array indexing and loop range

   Array indices 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 = 0; i <= n; i++) { sum += arr[i]; } uses i <= n, which accesses arr[n] (out-of-bounds). int sum = 0; for(int i = 1; i < n; i++) { sum += arr[i]; } starts at 1, missing arr[0]. int sum = 0; for(int i = n - 1; i >= 0; i--) { sum += arr[i]; } correctly sums all elements in reverse order, but the question asks for traversal in forward order. int sum = 0; for(int i = 0; i < n; i++) { sum += arr[i]; } correctly sums all elements from 0 to n-1 in forward order.

3. Final Answer:

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

4. Quick Check:

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

Hint: Sum elements by looping i from 0 to less than n [OK]

Common Mistakes:

• Using i <= n causing out-of-bounds
• Starting loop at 1 missing first element
• Looping backwards with wrong indices