C If ... Else

Conditions and If Statements

You have already learned that C supports the usual logical conditions from mathematics:

• 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.

we test two values to find out if 20 is greater than 18. If the condition is true, print some text:

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, and we know that 20 is greater than 18, we print to the screen that "x is greater than y".

The else Statement

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

The else if Statement

Use the else if statement to specify a new condition if the first condition is false.

Another Example

This example shows how you can use if..else to find out if a number is positive or negative: