5-cyclic structure

For the first few chapters, refer to: 1-Introduction 2-objective-c programming 3-classes, objects, and Methods 4-data types and expressions. We suggest you be familiar with the C language and Java language, quickly and easily passed this chapter. It's so painful for me to see things I know n years ago. It can only be used as a review. One of the basic attributes of a computer is that it can execute a group of statements repeatedly. This sentence is very difficult. The for statement is executed in the following steps: 1. Evaluate the value of the initial expression first. 2. Calculate the value of the cyclic condition. 3. Execute the program statement that forms the loop body. 4. Evaluate the value of the loop expression. 5. Return to 2 for execution. If you execute a break statement in a set of nested loops, only the innermost loop that executes the break statement is introduced.