Why variables are needed in C - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an integer variable named age.

C

int [1];

Drag options to blanks, or click blank then click option'

Aage

B5

Cmain

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number instead of a name.

Using a reserved word like main.

Variables store data. Here, age is the name of the variable.

2fill in blank

medium

Complete the code to assign the value 10 to the variable count.

C

count [1] 10;

Drag options to blanks, or click blank then click option'

A=

B!=

C+=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of = for assignment.

Using != which means 'not equal'.

The single equals sign = assigns a value to a variable.

3fill in blank

hard

Fix the error in the code to declare a variable named score of type integer.

C

[1] score;

Drag options to blanks, or click blank then click option'

Ainteger

Bfloat

Cint

Dchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using integer instead of int.

Using float or char which are different types.

In C, int is the correct keyword for integer variables.

4fill in blank

hard

Fill both blanks to declare a variable height of type float and assign it the value 1.75.

C

[1] [2] = 1.75;

Drag options to blanks, or click blank then click option'

Afloat

Bheight

Cint

Dweight

Attempts:

3 left

💡 Hint

Common Mistakes

Using int for decimal values.

Using wrong variable names.

float declares a decimal number variable, and height is the variable name.

5fill in blank

hard

Fill all three blanks to declare an integer variable total, assign 100 to it, and then print it using printf.

C

int [1];
[2] = 100;
printf("%d\n", [3]);

Drag options to blanks, or click blank then click option'

Acount

Btotal

Dscore

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in declaration and print.

Forgetting to declare the variable before use.

The variable total is declared, assigned, and printed. The same name is used consistently.

Practice

1. Why do we need variables in a C program?

easy

A. To create functions automatically

B. To make the program run faster by skipping calculations

C. To write comments inside the code

D. To store and manage data that can change during program execution

Solution

1. Step 1: Understand the role of variables

   Variables hold data values that can change while the program runs, allowing dynamic behavior.

2. Step 2: Compare other options

   Options B, C, and D describe unrelated tasks: speeding up code, commenting, and creating functions, which are not the purpose of variables.

3. Final Answer:

   To store and manage data that can change during program execution -> Option D

4. Quick Check:

   Variables store changing data = A [OK]

Hint: Variables hold changing data in programs [OK]

Common Mistakes:

• Thinking variables speed up the program
• Confusing variables with comments
• Believing variables create functions

2. Which of the following is the correct way to declare an integer variable named count in C?

easy

A. integer count;

B. int count;

C. count int;

D. var count;

Solution

1. Step 1: Recall C variable declaration syntax

   In C, the type comes first, then the variable name, ending with a semicolon. So int count; is correct.

2. Step 2: Check other options

   Options A, B, and D use incorrect order or invalid keywords not recognized in C.

3. Final Answer:

   int count; -> Option B

4. Quick Check:

   Type before name with semicolon = C [OK]

Hint: Type first, then variable name, end with semicolon [OK]

Common Mistakes:

• Writing variable name before type
• Using non-C keywords like 'integer' or 'var'
• Forgetting the semicolon

3. What will be the output of this C code?

int main() {
    int x = 5;
    x = x + 3;
    printf("%d", x);
    return 0;
}

medium

A. 5

B. 3

C. 8

D. 0

Solution

1. Step 1: Follow the variable update

   Variable x starts at 5, then 3 is added, so x becomes 8.

2. Step 2: Understand the print statement

   printf("%d", x); prints the current value of x, which is 8.

3. Final Answer:

   8 -> Option C

4. Quick Check:

   5 + 3 = 8 [OK]

Hint: Add values step-by-step to find final variable value [OK]

Common Mistakes:

• Printing initial value without update
• Confusing addition with assignment
• Ignoring the printf format specifier

4. Find the error in this C code snippet:

int main() {
    int number;
    number = 10
    printf("%d", number);
    return 0;
}

medium

A. Missing semicolon after assignment

B. Variable 'number' not declared

C. Incorrect printf format specifier

D. Missing return statement

Solution

1. Step 1: Check each line for syntax errors

   The line number = 10 is missing a semicolon at the end, which is required in C.

2. Step 2: Verify other parts

   The variable is declared, printf format is correct, and return statement is present, so no errors there.

3. Final Answer:

   Missing semicolon after assignment -> Option A

4. Quick Check:

   Every statement ends with semicolon = B [OK]

Hint: Check for missing semicolons after statements [OK]

Common Mistakes:

• Forgetting semicolon after assignment
• Assuming variable declaration is missing
• Misreading printf format

5. You want to store a user's age and then increase it by 1 to represent their next birthday. Which sequence of steps correctly uses variables in C?

hard

A. Declare an int variable, assign age, add 1 to variable, print variable

B. Declare a float variable, assign age, multiply by 2, print variable

C. Declare a string variable, assign age, add 1, print variable

D. Declare an int variable, assign age, subtract 1, print variable

Solution

1. Step 1: Choose correct variable type and operations

   Age is a whole number, so int is appropriate. Adding 1 represents the next birthday.

2. Step 2: Evaluate each option's logic

   Declare an int variable, assign age, add 1 to variable, print variable correctly declares an int, assigns age, adds 1, and prints. Others use wrong types or wrong operations.

3. Final Answer:

   Declare an int variable, assign age, add 1 to variable, print variable -> Option A

4. Quick Check:

   Use int and add 1 for next birthday = D [OK]

Hint: Use int for age and add 1 to update [OK]

Common Mistakes:

• Using float or string for age
• Subtracting instead of adding
• Multiplying age incorrectly