3 Everything is about control
This chapter covers
- Conditional execution with
if - Iterating over domains
- Making multiple selections
In our introductory example, listing 1.1, we saw two different constructs that allowed us to control the flow of a program’s execution: functions and the for iteration. Functions are a way to transfer control unconditionally. The call transfers control unconditionally to the function, and a return statement unconditionally transfers it back to the caller. We will come back to functions in chapter 7.
The for statement is different in that it has a controlling condition (i < 5 in the example) that regulates if/when the secondary block ({ printf(...) }) is executed. C has five conditional control statements: if, for, do, while, and switch. We will look at these statements in this section: if introduces a conditional execution depending on a Boolean expression; for, do, and while are different forms of iterations; and switch is a multiple selection based on an integer value.
C has some other conditionals that we will discuss later: the ternary operatorC, denoted by an expression in the form cond ? A : B (section 4.5); the compile-time preprocessor conditionals #if, #ifdef, #ifndef, #elif, #elifdef, #elifndef, #else, #endif (section 8.1.5); and type-generic expressions denoted with the keyword _Generic (chapter 18).
3.1 Conditional execution
The first construct that we will look at is specified by the keyword if. It looks like this: