C If ... Else

Conditions and If Statements

You already know that C supports familiar comparison conditions from mathematics, such as:

• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Equal to: a == b
• Not equal to: a != b

You can use these conditions to perform different actions for different decisions.

C has the following conditional statements:

• Use if to specify a block of code to be executed, if a specified condition is true
• Use else to specify a block of code to be executed, if the same condition is false
• Use else if to specify a new condition to test, if the first condition is false
• Use switch to specify many alternative blocks of code to be executed

The if Statement

Use the if statement to specify a block of code to be executed if a condition is true.

In the example below, we test two values to find out if 20 is greater than 18. If the condition is true, we print a message:

We can also test variables:

Example explained

In the example above we use two variables, x and y, to test whether x is greater than y (using the > operator). As x is 20 and y is 18, the condition is true, so the program prints "x is greater than y".

Using a Boolean Variable

Since the condition in an if statement must be either true or false, you can store the result in a boolean variable instead of writing the comparison directly:

This can make your code easier to read, especially when the condition is complex or used more than once.