What are the three basic program structures in C language?

The three basic program structures of the C language are: sequential structure, selection structure (branch structure), and loop structure. The sequential structure is executed sentence by sentence from beginning to end; the selection structure, after reaching a certain node, will decide which branch direction to execute next based on the result of a judgment; the loop structure has a loop body, and the loop body is a paragraph code.

The three basic program structures of the C language are: sequential structure, selection structure (branch structure), and loop structure;

1. Program structure: In C language programs, there are three program structures: sequential structure, selection structure (branch structure), and loop structure;

Sequential structure: execution sentence after sentence from beginning to end down until the last sentence is executed;

Selection structure: After reaching a certain node, the branch direction to be executed will be determined based on the result of a judgment;

Loop structure: Loop structure There is a loop body, and inside the loop body is a piece of code. For the loop structure, the key is to decide how many times the loop body is executed based on the judgment result;

Note: Logically there is a bool type (also called boolean type, Boolean type), which has only two values. , that is, true and false. The final value of the judgment expression in C language is a bool type. The bool value of this judgment expression determines how to select the selection structure and how to loop the loop structure;

2. Sequential structure: The sequential structure is very simple. Generally, in addition to selection structures and loop structures, what we encounter are sequential structures;

3. Selection structure: There are two main selection structures commonly used in C language:

(1 ) if else：Introduction of keywords: if 　　　　else if

　　if (bool值) 　　　　// 如果bool值为真，则执行代码段1，否则执行代码段2
　　　　{
　　　　　　代码段1
　　　　}
　　　　else
　　　　{
　　　　　　代码段2
　　　　}
　　　　if (bool值1)　　　　// 如果bool值1为真，则执行代码段1，否则判断bool值2是否为真
　　　　{
　　　　　　代码段1
　　　　}
　　　　else if (bool值2)　　// 若bool值2为真则执行代码段2，否则直接执行代码段3
　　　　{　　　　　　　　　　// 开头的if和结尾的else都只能有一个，但是中间的else if可以有好多个
　　　　　　代码段2
　　　　}
　　　　else
　　　　{
　　　　　　代码段3
　　　　}

(2) switch case：Introduction of keywords: switch　　case　break　default

switch (变量) 　　　　　　// 执行到这一句时，变量的值是已知的
　　　　{ 　　　　　　　　　　　　// switch case语句执行时，会用该变量的值依次与各个case后的常数去对比，试图找到第一个匹配项，找到匹配的项目后，
　　　　 　　case 常数1: 　　　　　　// 就去执行该case对应的代码段，如果没找到则继续下一个case，直到default
　　　　 　　　　代码段1;　　　　　　　　// 如果前面的case都未匹配，则default匹配。
　　　　 　　　　break;
　　　　　 　case 常数2:  
　　　　 　　　　代码段2;
　　　　 　　　　break;
　　　　 　　……
　　　　 　　default:
　　　　 　　　　代码段n;
　　　　 　　　　break;
　　　　}

Note:

First, the case must be a constant, and it must be an integer;

Second, generally speaking, after the code segment in each case There must be a break;

Thirdly, there is usually a default after the case. Although the syntax allows no default, it is recommended that you must write it when writing code;

Recommended tutorial: "C language tutorial》

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