Increment and decrement operators - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to increase the value of count by 1 using the increment operator.

C

int count = 5;
count[1];
printf("%d", count);

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

A+=

B--

C++

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using the decrement operator -- instead of increment.

Using += without specifying the value.

The increment operator ++ increases the value of a variable by 1.

2fill in blank

medium

Complete the code to decrease the value of num by 1 using the decrement operator.

C

int num = 10;
[1]num;
printf("%d", num);

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

A--

Bnum++

Attempts:

3 left

💡 Hint

Common Mistakes

Using the increment operator ++ instead of decrement.

Placing the operator after the variable when the problem expects before.

The decrement operator -- decreases the value of a variable by 1. Placing it before the variable decreases the value before use.

3fill in blank

hard

Fix the error in the code to correctly increment value by 1.

C

int value = 7;
value [1];
printf("%d", value);

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

A++value

B++

Cvalue+1

Dvalue++

Attempts:

3 left

💡 Hint

Common Mistakes

Writing just ++ without the variable.

Using value+1 which does not change the variable.

Using value++ increments the value after its current use. It is a correct way to increase by 1.

4fill in blank

hard

Fill both blanks to create a loop that decreases i from 5 to 1.

C

for(int i = 5; i [1] 0; i[2]) {
    printf("%d ", i);
}

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

A>

B<

C--

D++

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > in the condition.

Using ++ instead of -- in the update.

The loop runs while i is greater than 0 and decreases i by 1 each time using --.

5fill in blank

hard

Fill all three blanks to create a loop that prints numbers from 1 to 5 using increment.

C

for(int num = [1]; num [2] 5; num[3]) {
    printf("%d ", num);
}

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

A0

B<=

C++

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 0 instead of 1.

Using < instead of <= in the condition.

Using decrement operator instead of increment.

The loop starts at 1, runs while num is less than or equal to 5, and increments num by 1 each time.

Practice

1. What does the ++ operator do in C?

easy

A. Adds 1 to the variable

B. Subtracts 1 from the variable

C. Multiplies the variable by 2

D. Divides the variable by 2

Solution

1. Step 1: Understand the meaning of ++

   The ++ operator increases the value of a variable by 1.

2. Step 2: Compare with other options

   Subtracting, multiplying, or dividing are not what ++ does.

3. Final Answer:

   Adds 1 to the variable -> Option A

4. Quick Check:

   ++ means add 1 [OK]

Hint: Remember ++ means add one, -- means subtract one [OK]

Common Mistakes:

• Confusing ++ with --
• Thinking ++ multiplies
• Mixing increment with assignment

2. Which of the following is the correct syntax for prefix decrement of a variable x by 1 in C?

easy

A. x--;

B. x-+;

C. x+-;

D. --x;

Solution

1. Step 1: Identify prefix decrement syntax

   The prefix decrement operator is --x;, which decrements x by 1.

2. Step 2: Check options carefully

   A is postfix x--;, B x-+; and C x+-; invalid syntax, D is correct prefix.

3. Final Answer:

   --x; -> Option D

4. Quick Check:

   Prefix decrement --x; is correct syntax [OK]

Hint: Look for correct -- syntax before or after variable [OK]

Common Mistakes:

• Using invalid operators like -+ or +-
• Confusing prefix and postfix syntax
• Missing semicolon

3. What is the output of this C code?

int x = 5;
printf("%d", x++);
printf(" %d", x);

medium

A. 5 5

B. 5 6

C. 6 6

D. 6 5

Solution

1. Step 1: Understand postfix increment x++

   Postfix means use the current value first, then add 1. So printf("%d", x++) prints 5, then x becomes 6.

2. Step 2: Print updated value of x

   The second printf prints the new value of x, which is 6.

3. Final Answer:

   5 6 -> Option B

4. Quick Check:

   Postfix prints old value, then increments [OK]

Hint: Postfix ++ prints old value, prefix ++ prints new value [OK]

Common Mistakes:

• Confusing postfix with prefix
• Expecting increment before print
• Ignoring space in output

4. Find the error in this code snippet:

int a = 3;
int b = ++a++;
printf("%d", b);

medium

A. Syntax error due to invalid use of increment operators

B. b will be 4

C. b will be 5

D. No error, prints 3

Solution

1. Step 1: Analyze the expression ++a++

   This expression tries to apply prefix and postfix increment operators together on the same variable, which is invalid syntax in C.

2. Step 2: Understand compiler rules

   C does not allow chaining increments like this; it causes a syntax error.

3. Final Answer:

   Syntax error due to invalid use of increment operators -> Option A

4. Quick Check:

   Invalid chaining of ++ operators causes syntax error [OK]

Hint: Don't chain prefix and postfix ++ on same variable [OK]

Common Mistakes:

• Thinking it increments twice
• Ignoring syntax error
• Assuming valid output

5. Consider this code:

int arr[3] = {1, 2, 3};
int i = 0;
int sum = 0;
while (i < 3) {
    sum += arr[i++];
}
printf("%d", sum);

What is the output and why?

hard

A. 6 because i increments before accessing each element

B. 5 because i increments before accessing each element

C. 6 because i increments after accessing each element

D. 5 because i increments after accessing each element

Solution

1. Step 1: Understand postfix increment in arr[i++]

   The value of i is used first to access the array element, then i is incremented.

2. Step 2: Calculate sum step-by-step

   Elements accessed: arr[0]=1, arr[1]=2, arr[2]=3; sum = 1+2+3 = 6.

3. Final Answer:

   6 because i increments after accessing each element -> Option C

4. Quick Check:

   Postfix increments after use, sum is 6 [OK]

Hint: Postfix increments after use, so sum all elements correctly [OK]

Common Mistakes:

• Confusing prefix and postfix increments
• Calculating wrong sum
• Assuming i increments before access