Shulou(Shulou.com)06/03 Report--

This article mainly introduces the C language branch and loop statement example analysis, the article is very detailed, has a certain reference value, interested friends must read!

- if statement: if (expression)

//put an expression in parentheses

//expression is true if the result of the expression is nonzero

//expression result is zero, expression is false

If statements can be single-branched, double-branched, multi-branched, and can also be executed after being enclosed in braces. The following figure is an example of double-branching:

if(expression) statements;//each semicolon separated is called a statement else //Attention! Write without braces and execute only one statement

The following is an example of multiple branches:

if(expression)//the first statement also has no semicolon statement;else if(expression); statement;//note that the else if statement ends with a semicolon else if(expression); Sentence://omit several else ifelse here//here is the last sentence, no semicolon statements;

The following is an example of executing multiple statements:

if(expression){ statement 01; statement 02; //....}// The following can be a single branch, two branches or multiple branches hanging else problem

Examples:

#include int main(){ int a = 0; int b = 2; if(a == 1) if (b == 2) printf("hehe\n"); else printf("haha\n"); return 0;}

Most people will probably say, at first glance, that the screen will print: haha, because they will think that after the expression in line 6, a is not equal to 1, so the expression is false, and execute the statement after else. But otherwise, else only matches the closest if, so the actual print result of the above code is: no print.

So good code writing style can greatly reduce unnecessary misunderstandings

//correct writing if(a == 1) if(b == 2) printf("hehe\n"); else printf("haha\n");- switch statement

The switch statement is also a branch statement, mostly used in multi-branch situations.

The syntax of the switch statement:

switch(integer expression)//no semicolon required {case (integer constant expression): statements; break;//break determines whether the program should go down after reaching this position//jump out of switch directly with break//continue to execute other case statements without break//until it encounters break}

Details to note:

(Take the code as an example)

#include int main(){ int day = 0; scanf("%d",&day); switch (day) { case 1: //Below } return 0;} Details to watch out for

(compare above)

If you change the code in line 4 to: float day, then the program will not continue to execute, because after this change, the original day will be changed to a floating point type, and the day will still be a floating point type after passing to line 6. The syntax of using switch clearly stipulates: switch (), integer constant expressions must be written in parentheses, and integers and constants must be written.

Also, if you define an integer variable in advance at the beginning of the switch statement execution, assign it a value, and then put this variable after the case, this program cannot be executed. The following example:

int n = 1;switch (/* here */){ case n://The above operation must cause the compiler to report an error//because n is essentially a variable//after the case, it must be an integer and constant according to the syntax specification}

In addition, if the case followed by integer, constant, and is an expression, then it is also executable down the '

//Example case 1+0://This is also compilable

Finally, if the case is followed by a character type, it can also be compiled, because the character is also a type of plastic, and the character is stored in the computer in the form of ascii code.

Default clause in switch:

This clause applies to inputs that are processed outside of all branching cases

Examples:

//redundant code abbreviated int day = 0;scanf("%d".& day);switch(day){ case 1://statements and breaks in case are abbreviated case 2: case 3: case 4: case 5: case 6: case 7: default: printf("input error\n"); break; }

As shown in the figure above, there are only seven branches in the case statement to choose from, but if the input accidentally enters an error and does not enter a number from 1 to 7 (such as entering a 9), then the program will not compile at the end. To prevent this from happening, a default clause is specially designed for those other error cases to enter, giving the input an error prompt. In addition, default clauses can be placed at the beginning or end of sentences, but we usually place them at the end of sentences by default.

Loop statements: loop structure is divided into three types: while loop, for loop, do while loop

- while loop syntax structure while(//expression, i.e. condition for judging loop execution){ loop statement;}

If the result of the above expression is true, that is, non-zero, then loop execution

If the expression results in false, i.e. 0, then the loop body does not execute

Notes:

If there is a break in the while loop, the break is used to call up the current loop body.

That is to say, it can only jump one level and jump out of the current cycle. If there's a loop out there, it's still going on.

If there is a continue in the while loop, then the function of continue is to skip the code behind the continue and go directly to the judgment part at the beginning of the program to see if you want to continue executing the code. The example is as follows:

//The redundant part of the code is slightly while (i 10)), and the adjustment part (i ++) is sometimes very far apart. If you need to change it, it will be easy to change it.

In a for loop, expression 1 is used to give an initial value to the loop variable (expression 1 will only be executed once, and will not be used later. The variable retains the previous value before each loop starts, unless the loop itself is in another loop, in which case it will be initialized once each time, so in general, when it comes up again, the loop variable will only go through expression 2 and expression 3 to judge itself, and then continue to execute the following code). Expression 2 is used for judgment, and Expression 3 is used for adjustment.

Points to note: Try not to change loop variables in the loop body, otherwise the loop is easy to lose control, the following code block for example:

#include int main(){ for(i=0; i

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