What is and how to use the conditional IF-ELSE in C#

The if and if-else conditionals are fundamental control structures that allow making decisions based on boolean evaluations (true or false).

The IF Conditional

The if structure evaluates a boolean expression and executes a block of code only if the expression is true. The basic syntax of an if conditional in C# is:

if (condition)
{
    // Code to execute if the condition is true
}

Let’s see it with an example,

int number = 10;

if (number > 5)
{
    Console.WriteLine("The number is greater than 5");
}

In this example, the condition number > 5 evaluates to true, so the message “The number is greater than 5” is printed to the console.

The IF ELSE Conditional

The if conditional allows adding an else block of alternative code that will execute if the if condition is false. The basic syntax is:

if (condition)
{
    // Code to execute if the condition is true
}
else
{
    // Code to execute if the condition is false
}

Let’s see it with an example,

int number = 3;

if (number > 5)
{
    Console.WriteLine("The number is greater than 5");
}
else
{
    Console.WriteLine("The number is not greater than 5");
}

In this case,

• The condition number > 5 is false
• So the block of code inside the else executes
• Therefore, “The number is not greater than 5” is printed to the console

The IF ELSE-IF Conditional

To evaluate multiple conditions, you can chain multiple if / else-if / else blocks. This allows evaluating several conditions in sequence until one of them is true.

if (condition1)
{
    // Code to execute if condition1 is true
}
else if (condition2)
{
    // Code to execute if condition1 is false and condition2 is true
}
else
{
    // Code to execute if all previous conditions are false
}

Using Logical Operators in Conditionals

To evaluate multiple conditions within a single if, you can use logical operators like && (logical AND) and || (logical OR).

For example, the && operator evaluates to true only if both conditions are true.

int number = 10;

if (number > 5 && number < 15)
{
    Console.WriteLine("The number is between 5 and 15");
}

While the || operator evaluates to true if at least one of the conditions is true.

int number = 20;

if (number < 5 || number > 15)
{
    Console.WriteLine("The number is less than 5 or greater than 15");
}

Practical Examples

Determine if a number is less than 5 or greater than 15

In this example, we determine if a number is less than 5, greater than 15, or within the intermediate range.

// Declare an integer variable
int number = 10;

// Evaluate if the number is greater than 15
if (number > 15)
{
    // If it is greater than 15, print this message
    Console.WriteLine("The number is greater than 15");
}
// Evaluate if the number is greater than 5 but not greater than 15
else if (number > 5)
{
    // If it is greater than 5 but less than or equal to 15, print this message
    Console.WriteLine("The number is greater than 5 but less than or equal to 15");
}
else
{
    // If the number is not greater than 5, print this message
    Console.WriteLine("The number is 5 or less");
}

Here, we sequentially evaluate the conditions:

• number > 15 is false
• but number > 5 is true
• Therefore, “The number is greater than 5 but less than or equal to 15” is printed.

Determine the largest of three numbers

In this example, we find the largest of three numbers using if-else structures.

// Declare three integer variables and a variable to store the largest value
int a = 5, b = 10, c = 3;
int largest;

if (a > b && a > c)  // Evaluate if 'a' is greater than 'b' and 'c'
{
    largest = a;  // If 'a' is the largest, assign 'a' to the variable 'largest'
}

else if (b > a && b > c)  // Evaluate if 'b' is greater than 'a' and 'c'
{  
    largest = b;  // If 'b' is the largest, assign 'b' to the variable 'largest'
}
else
{  
    largest = c;  // If 'c' is the largest, assign 'c' to the variable 'largest'
}

// Print the largest number
Console.WriteLine($"The largest number is: {largest}");

Check grade ranges

In this example, we assign a letter grade based on a numeric score using a series of if-else conditions.

// Declare an integer variable for the grade and a string variable for the range
int grade = 85;
string range;

if (grade >= 90)  // Evaluate if the grade is 90 or higher
{
    range = "A"; // If the grade is 90 or higher, assign 'A' to the range
}
else if (grade >= 80)  // Evaluate if the grade is 80 or higher
{
    range = "B";  // If the grade is 80 or higher, assign 'B' to the range
}
else if (grade >= 70) // Evaluate if the grade is 70 or higher
{
    range = "C"; // If the grade is 70 or higher, assign 'C' to the range
}
else if (grade >= 60)  // Evaluate if the grade is 60 or higher
{
    range = "D"; // If the grade is 60 or higher, assign 'D' to the range
}
else
{
    range = "F"; // If the grade is less than 60, assign 'F' to the range
}

// Print the grade range
Console.WriteLine($"The grade is: {range}");