C# Program to Check Positive, Negative, or Zero

Use if statements in C# to check if a number is positive, negative, or zero like this: if (num > 0) { Console.WriteLine("Positive"); } else if (num < 0) { Console.WriteLine("Negative"); } else { Console.WriteLine("Zero"); }.

Examples

Input5

OutputPositive

Input-3

OutputNegative

Input0

OutputZero

How to Think About It

To decide if a number is positive, negative, or zero, first compare it with zero using > and < operators. If it is greater than zero, it is positive; if less, it is negative; otherwise, it is zero.

Algorithm

1

Get the input number.

2

Check if the number is greater than zero.

3

If yes, print 'Positive'.

4

Else, check if the number is less than zero.

5

If yes, print 'Negative'.

6

Otherwise, print 'Zero'.

Code

csharp

using System;
class Program {
    static void Main() {
        Console.Write("Enter a number: ");
        int num = int.Parse(Console.ReadLine());
        if (num > 0) {
            Console.WriteLine("Positive");
        } else if (num < 0) {
            Console.WriteLine("Negative");
        } else {
            Console.WriteLine("Zero");
        }
    }
}

Output

Enter a number: 5
Positive

Dry Run

Let's trace input 5 through the code

1

Input

User enters 5, so num = 5

2

Check if num > 0

5 > 0 is true

3

Print result

Print 'Positive'

Step	Condition	Result
Check num > 0	5 > 0	true
Print output	Positive	Printed

Why This Works

Step 1: Compare with zero

The program uses if to check if the number is greater than zero to identify positive numbers.

Step 2: Check for negative

If the number is not positive, it checks if it is less than zero to find negative numbers.

Step 3: Handle zero

If neither positive nor negative, the number must be zero, so it prints 'Zero'.

Alternative Approaches

Using switch expression (C# 8.0+)

csharp

using System;
class Program {
    static void Main() {
        Console.Write("Enter a number: ");
        int num = int.Parse(Console.ReadLine());
        string result = num switch {
            > 0 => "Positive",
            < 0 => "Negative",
            _ => "Zero"
        };
        Console.WriteLine(result);
    }
}

This approach uses a modern switch expression for cleaner code but requires C# 8.0 or later.

Using ternary operator

csharp

using System;
class Program {
    static void Main() {
        Console.Write("Enter a number: ");
        int num = int.Parse(Console.ReadLine());
        string result = num > 0 ? "Positive" : (num < 0 ? "Negative" : "Zero");
        Console.WriteLine(result);
    }
}

This uses nested ternary operators for a compact form but can be harder to read for beginners.

Complexity: O(1) time, O(1) space

Time Complexity

The program performs a fixed number of comparisons regardless of input size, so it runs in constant time O(1).

Space Complexity

It uses a fixed amount of memory for variables and does not allocate extra space, so space complexity is O(1).

Which Approach is Fastest?

All approaches run in constant time; the choice depends on readability and language version support.

Approach	Time	Space	Best For
If-else statements	O(1)	O(1)	Beginners and clarity
Switch expression	O(1)	O(1)	Modern syntax, cleaner code
Ternary operator	O(1)	O(1)	Compact code, experienced users