Relational operators in C - Step-by-Step Execution

Concept Flow - Relational operators

Start

↓

Evaluate operands

↓

Apply relational operator

↓

Result: true (1) or false (0)

↓

Use result in expression or decision

↓

End

Relational operators compare two values and return 1 if true or 0 if false, which can be used in decisions.

Execution Sample

C

int a = 5;
int b = 3;
int result = a > b;
printf("%d", result);

Compares if a is greater than b and prints 1 if true, 0 if false.

Execution Table

Step	Expression	Operands	Evaluation	Result	Output
1	a > b	a=5, b=3	5 > 3	true (1)	1
2	End	-	-	-	-

💡 Program ends after printing the result of the relational comparison.

Variable Tracker

Variable	Start	After Step 1	Final
a	5	5	5
b	3	3	3
result	undefined	1	1

Key Moments - 2 Insights

Why does the relational operator return 1 or 0 instead of true or false?

In C, relational operators return integer 1 for true and 0 for false, as shown in execution_table step 1, because C uses integers to represent boolean values.

What happens if both operands are equal with the '>' operator?

If operands are equal, the '>' operator returns 0 (false), because the condition is not true. This would be seen in execution_table if a and b were equal.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'result' after step 1?

A 1

B 0

C 5

D 3

💡 Hint

Check the 'Result' column in execution_table row 1.

At which step does the program print the output?

A Step 2

B Before Step 1

C Step 1

D No output is printed

💡 Hint

Look at the 'Output' column in execution_table row 1.

If 'a' was 2 and 'b' was 3, what would 'result' be after step 1?

A 1

B 0

C 2

D 3

💡 Hint

Relational operator '>' returns 1 if left operand is greater, else 0.

Concept Snapshot

Relational operators compare two values.
Operators: >, <, >=, <=, ==, !=
Return 1 if true, 0 if false.
Used in conditions and expressions.
Example: int r = a > b; // r is 1 if a > b else 0

Full Transcript

This lesson shows how relational operators work in C. They compare two values and return 1 if the comparison is true or 0 if false. For example, 'a > b' checks if a is greater than b. If a is 5 and b is 3, 'a > b' is true, so the result is 1. This result can be stored in a variable or used in decisions like if statements. The execution table traces the comparison step by step, showing operands, evaluation, and output. Variables a and b keep their values, while result stores the comparison outcome. Beginners often wonder why the result is 1 or 0 instead of true or false; in C, 1 and 0 represent true and false respectively. Another common question is what happens if values are equal; the operator returns 0 because the condition is false. The quiz asks about the result value, when output is printed, and what happens if values change. Remember, relational operators are essential for making decisions in programs.

Practice

1. Which of the following relational operators in C checks if two values are equal?

easy

A. !=

B. ==

C. =

D. >

Solution

1. Step 1: Understand the purpose of each operator

   The operator == is used to compare two values for equality. The single = is an assignment operator, != checks inequality, and > checks if left is greater than right.

2. Step 2: Identify the equality operator

   Since == compares two values for equality, it is the correct relational operator for this purpose.

3. Final Answer:

   == -> Option B

4. Quick Check:

   Equality check = == [OK]

Hint: Equality uses double equals ==, not single = [OK]

Common Mistakes:

• Confusing = (assignment) with == (equality)
• Using != instead of ==
• Using > instead of ==

2. Which of the following is the correct syntax to check if variable a is not equal to variable b in C?

easy

A. a !== b

B. a <> b

C. a =! b

D. a != b

Solution

1. Step 1: Recall the correct not equal operator in C

   In C, the operator for not equal is !=. Other options like <> or !== are not valid in C.

2. Step 2: Verify the syntax correctness

   The expression a != b correctly compares if a is not equal to b.

3. Final Answer:

   a != b -> Option D

4. Quick Check:

   Not equal operator = != [OK]

Hint: Use != for not equal in C, not <> or !== [OK]

Common Mistakes:

• Using <> which is invalid in C
• Writing =! instead of !=
• Using !== which is from other languages

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

int a = 5, b = 10;
if (a > b) {
    printf("True\n");
} else {
    printf("False\n");
}

medium

A. True

B. 5

C. False

D. 10

Solution

1. Step 1: Evaluate the relational expression a > b

   Variable a is 5 and b is 10. Since 5 is not greater than 10, the expression a > b is false.

2. Step 2: Determine which branch executes

   Because the condition is false, the else block runs, printing "False".

3. Final Answer:

   False -> Option C

4. Quick Check:

   5 > 10 = false [OK]

Hint: Compare values carefully; 5 > 10 is false [OK]

Common Mistakes:

• Assuming 5 > 10 is true
• Confusing else and if blocks
• Ignoring relational operator meaning

4. Identify the error in the following C code snippet:

int x = 7, y = 3;
if (x =< y) {
    printf("x is less or equal to y\n");
}

medium

A. Using =< instead of <=

B. Missing semicolon after if condition

C. Using assignment operator inside if

D. Incorrect printf syntax

Solution

1. Step 1: Check the relational operator syntax

   The operator =< is invalid in C. The correct operator for less than or equal is <=.

2. Step 2: Confirm other syntax correctness

   The semicolon after if condition is not needed, assignment operator is not used here, and printf syntax is correct.

3. Final Answer:

   Using =< instead of <= -> Option A

4. Quick Check:

   Less or equal operator is <=, not =< [OK]

Hint: Remember <= for less or equal, not =< [OK]

Common Mistakes:

• Swapping <= to =<
• Adding semicolon after if condition
• Confusing assignment = with comparison ==

5. Given the code below, what will be the output?

int a = 4, b = 4, c = 5;
if (a == b && b < c) {
    printf("Yes\n");
} else {
    printf("No\n");
}

Choose the correct output considering relational operators combined with logical operators.

hard

A. Yes

B. No

C. 4

D. Syntax Error

Solution

1. Step 1: Evaluate the first condition a == b

   Both a and b are 4, so a == b is true.

2. Step 2: Evaluate the second condition b < c

   b is 4 and c is 5, so b < c is true.

3. Step 3: Combine conditions with logical AND

   Both conditions are true, so the combined condition is true, executing the if block.

4. Final Answer:

   Yes -> Option A

5. Quick Check:

   (4 == 4) && (4 < 5) = true [OK]

Hint: Both conditions must be true for && to print Yes [OK]

Common Mistakes:

• Ignoring logical AND meaning
• Mixing up == and =
• Assuming false when both conditions true