Logical operators - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of combined logical AND and OR

What is the output of this C code snippet?

C

#include <stdio.h>

int main() {
    int a = 5, b = 0, c = 3;
    int result = a && b || c;
    printf("%d", result);
    return 0;
}

A 0

B 1

C 3

D 5

💡 Hint

Remember that in C, logical AND (&&) and OR (||) return 1 or 0, not the original values.

The expression a && b evaluates to 0 because b is 0 (false). Then 0 || c evaluates to 1 because c is non-zero (true). So the final result is 1.

❓ Predict Output

intermediate

Logical NOT operator effect

What will this C program print?

C

#include <stdio.h>

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

A 1

B 0

C -1

D Garbage value

💡 Hint

Logical NOT (!) returns 1 if the operand is zero, else 0.

Since x is 0 (false), !x is 1 (true). So the program prints 1.

❓ Predict Output

advanced

Short-circuit evaluation in logical AND

What is the output of this C code?

C

#include <stdio.h>

int main() {
    int a = 0, b = 5;
    int result = a && (++b);
    printf("%d %d", result, b);
    return 0;
}

A 1 5

B 0 6

C 0 5

D 1 6

💡 Hint

Logical AND stops evaluating if the first operand is false.

Since a is 0 (false), ++b is not evaluated due to short-circuit. So result is 0 and b remains 5.

❓ Predict Output

advanced

Short-circuit evaluation in logical OR

What will this program print?

C

#include <stdio.h>

int main() {
    int a = 1, b = 5;
    int result = a || (++b);
    printf("%d %d", result, b);
    return 0;
}

A 1 5

B 0 5

C 1 6

D 0 6

💡 Hint

Logical OR stops evaluating if the first operand is true.

Since a is 1 (true), ++b is not evaluated due to short-circuit. So result is 1 and b remains 5.

🧠 Conceptual

expert

Understanding logical operator precedence

Given the expression in C: int x = 0 || 1 && 0 || 1; What is the value of x after this line executes?

A 0

B 2

C Compiler error

D 1

💡 Hint

Remember that && has higher precedence than || in C.

The expression is evaluated as 0 || (1 && 0) || 1 = 0 || 0 || 1 = 1.