One-dimensional arrays in C - Mini Project: Build & Apply

Working with One-Dimensional Arrays in C

📖 Scenario: You are helping a small store keep track of the number of items sold each day over a week. You will use a one-dimensional array to store these daily sales numbers.

🎯 Goal: Build a simple C program that stores daily sales in an array, calculates the total sales for the week, and prints the total.

📋 What You'll Learn

Create an integer array named daily_sales with exactly 7 elements representing sales for each day of the week.

Create an integer variable named total_sales to hold the sum of all sales.

Use a for loop with the variable i to iterate over the daily_sales array.

Add each element of daily_sales to total_sales inside the loop.

Print the value of total_sales using printf.

💡 Why This Matters

🌍 Real World

Stores and small businesses often track daily sales to understand their performance and plan inventory.

💼 Career

Knowing how to use arrays and loops is essential for programming tasks involving data collection and processing in many software development jobs.

1

Create the sales array

Create an integer array called daily_sales with these exact values: 5, 8, 6, 7, 10, 9, 4.

C

# Create the integer array daily_sales with 7 elements
# Your code here

Hint

Use curly braces {} to list the values inside the array.

2

Create the total sales variable

Create an integer variable called total_sales and set it to 0.

C

int daily_sales[7] = {5, 8, 6, 7, 10, 9, 4};
# Create an integer variable total_sales and set it to 0
# Your code here

Hint

Initialize total_sales to zero before adding values.

3

Sum the sales using a for loop

Use a for loop with the variable i to iterate from 0 to 6 inclusive. Inside the loop, add daily_sales[i] to total_sales.

C

int daily_sales[7] = {5, 8, 6, 7, 10, 9, 4};
int total_sales = 0;
# Use a for loop to add each daily_sales element to total_sales
# Your code here

Hint

Use total_sales += daily_sales[i]; inside the loop to add each day's sales.

4

Print the total sales

Use printf to print the text Total sales: followed by the value of total_sales and a newline.

C

int daily_sales[7] = {5, 8, 6, 7, 10, 9, 4};
int total_sales = 0;
for (int i = 0; i < 7; i++) {
    total_sales += daily_sales[i];
}
# Print the total_sales value with a message
# Your code here

Hint

Use printf("Total sales: %d\n", total_sales); to print the result.

Practice

1. What is the starting index of a one-dimensional array in C?

easy

A. 0

B. 1

C. -1

D. Depends on the array size

Solution

1. Step 1: Understand array indexing in C

   In C, arrays always start indexing from 0, meaning the first element is at index 0.

2. Step 2: Confirm the starting index

   This is a fixed rule in C and does not depend on array size or other factors.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   Array indexing starts at 0 [OK]

Hint: Remember: C arrays always start at zero index [OK]

Common Mistakes:

• Thinking arrays start at 1 like in some other languages
• Assuming negative indexes are valid
• Believing index depends on array size

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

easy

A. int arr = 5;

B. int arr();

C. array int arr[5];

D. int arr[5];

Solution

1. Step 1: Recall C array declaration syntax

   In C, arrays are declared by specifying the type, name, and size in square brackets, like int arr[5];

2. Step 2: Check each option

   int arr[5]; matches the correct syntax. int arr(); uses parentheses which is for functions. int arr = 5; assigns a single int, not an array. array int arr[5]; uses invalid keyword 'array'.

3. Final Answer:

   int arr[5]; -> Option D

4. Quick Check:

   Array declaration uses square brackets [OK]

Hint: Use square brackets for array size in declaration [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Assigning a single value instead of declaring array
• Using invalid keywords like 'array'

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

int arr[3] = {10, 20, 30};
printf("%d", arr[1]);

medium

A. 10

B. 30

C. 20

D. Compilation error

Solution

1. Step 1: Identify the array elements and indexes

   The array arr has elements: arr[0]=10, arr[1]=20, arr[2]=30.

2. Step 2: Understand the printf statement

   printf prints the value at arr[1], which is 20.

3. Final Answer:

   20 -> Option C

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Remember array index 1 is second element [OK]

Common Mistakes:

• Confusing index 1 with index 0
• Expecting output 10 or 30 incorrectly
• Thinking code causes compilation error

4. Find the error in this code snippet:

int arr[4];
arr[4] = 10;

medium

A. Array index out of bounds

B. Missing semicolon

C. Wrong data type

D. No error

Solution

1. Step 1: Check array size and indexing

   The array arr has size 4, so valid indexes are 0,1,2,3 only.

2. Step 2: Identify the invalid index usage

   arr[4] accesses the fifth element, which is outside the array bounds causing undefined behavior.

3. Final Answer:

   Array index out of bounds -> Option A

4. Quick Check:

   Index must be less than array size [OK]

Hint: Index must be less than array size [OK]

Common Mistakes:

• Using index equal to array size
• Ignoring zero-based indexing
• Assuming no error for out-of-bounds access

5. Given the array declaration int nums[5] = {1, 2, 3, 4, 5};, which code snippet correctly calculates the sum of all elements?

hard

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

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

C. int sum = 0;
for(int i = 1; i < 5; i++) sum += nums[i];

D. int sum = 0;
for(int i = 0; i < 4; i++) sum += nums[i];

Solution

1. Step 1: Understand array size and valid indexes

   The array nums has 5 elements with indexes 0 to 4.

2. Step 2: Analyze each loop condition

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

3. Final Answer:

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

4. Quick Check:

   Loop from 0 to less than size sums all elements [OK]

Hint: Loop from 0 to less than array size for all elements [OK]

Common Mistakes:

• Using <= size causing out-of-bounds access
• Starting loop at 1 missing first element
• Stopping loop early missing last element