C language judgment, ternary operation and switch statement usage

Catalog

Judgment statement

? : Operator ( Ternary operator )

switch sentence

nesting switch sentence  

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Judgment statement

C Language provides the following types of judgment statements .

sentence	describe
if sentence	One  if sentence   Consists of a Boolean expression followed by one or more statements .
if...else sentence	One  if sentence   You can follow with an optional  else sentence ,else Statement is executed when the Boolean expression is false .
nesting if sentence	You can be in a  if  or  else if  Use another  if  or  else if  sentence .
switch sentence	One  switch  Statement allows testing when a variable is equal to more than one value .
nesting switch sentence	You can be in a  switch  Use another  switch  sentence .

? : Operator ( Ternary operator )

The general form is as follows ：

Exp1 ? Exp2 : Exp3;

among ,Exp1、Exp2 and Exp3 Is an expression . Please note that , Use and location of colons .

? The value of the expression is determined by Exp1 Decisive . If Exp1 It's true , The calculation Exp2 Value , The result is the value of the entire expression . If Exp1 For false , The calculation Exp3 Value , The result is the value of the entire expression .

switch sentence

One  switch  Statement allows testing when a variable is equal to more than one value . Each value is called a case, And the variables to be tested will be applied to each  switch case  Inspection .

grammar

C In language  switch  Sentence syntax ：

switch(expression){
    case constant-expression  :
       statement(s);
       break; /*  Optional  */
    case constant-expression  :
       statement(s);
       break; /*  Optional  */
  
    /*  You can have any number of  case  sentence  */
    default : /*  Optional  */
       statement(s);
}

 switch  Statements must follow the following rules ：

• switch  Statement  expression  Is a constant expression , Must be an integer or enumeration type .
• In a switch There can be any number of case sentence . Every case Followed by a value to compare and a colon .
• case Of  constant-expression  Must be with switch Variables in have the same data type , And it must be a constant or literal quantity .
• When the variable being tested equals case When the constant in ,case The following statement will be executed , Until I met  break  The statement so far .
• When you meet  break  When the sentence is ,switch End , The control flow will jump to switch The next line after the statement .
• Not every one case All need to include  break. If case The statement does not contain  break, The control flow will continue Follow up case, Until I met break until .
• One  switch  Statements can have an optional  default case, Appear in the switch Ending .default case Can be used on all of the above case To perform a task when it's not true .default case Medium  break  Statements are not required .

// example 
#include <stdio.h>
 
int main ()
{
   /*  Definition of local variables  */
   char grade = 'B';
 
   switch(grade)
   {
   case 'A' :
      printf(" great ！\n" );
      break;
   case 'B' :
   case 'C' :
      printf(" well done \n" );
      break;
   case 'D' :
      printf(" You passed \n" );
      break;
   case 'F' :
      printf(" Better try again \n" );
      break;
   default :
      printf(" Invalid grades \n" );
   }
   printf(" Your score is  %c\n", grade );
 
   return 0;
}

  When the above code is compiled and executed , It will produce the following results ：

 well done 
 Your score is  B

nesting switch sentence  

You can put a  switch  As an external  switch  Part of a sequence of statements , That is, it can be in a  switch  Use another  switch  sentence . Even inside and outside switch Of case Constants contain common values , There's no contradiction .

grammar

C In language   nesting switch  Sentence syntax ：

switch(ch1) {
   case 'A': 
      printf(" This  A  It's the outside  switch  Part of " );
      switch(ch2) {
         case 'A':
            printf(" This  A  It's internal  switch  Part of " );
            break;
         case 'B': /*  Inside  B case  Code  */
      }
      break;
   case 'B': /*  external  B case  Code  */
}

// example 
//switch  Statement nesting , Test length of service reward applet ！
#include<stdio.h>
int main(void)
{
    char sex;
    int age  ;
    printf(" Please enter your gender abbreviation ！ male (M), Woman (F)\n");
    scanf_s("%c", &sex);
    switch (sex)
    {
    case 'M':
    case 'm':
    printf(" Your gender is “ male ” Please enter the test !\n");
    printf(" Please enter your length of service ！\n");
    scanf_s("%2d",&age);
        switch (age)
        { 
        case 5:
            printf(" Reward iphone a ！！\n");
            break;
        case 10:
            printf(" Reward a car ！！\n");
            break;
        case 15:
            printf(" Reward a small building ！！\n");
            break;
        default:
            printf(" I'm sorry , Fail to meet the reward conditions or exceed the length of service ！！\n");
            break;
        }
    break;
    case 'F':
    case 'f':
        printf(" Your gender is “ Woman ” Please enter the test !\n");
        printf(" Please enter and exit your seniority ！\n");
        scanf_s("%2d",&age);
        switch (age)
        {
        case 5:
            printf(" Reward iphone a ！\n");
            break;
        case 10:
            printf(" Reward a set of famous brand cosmetics ！\n");
            break;
        case 15:
            printf(" Reward Hermes with a bag ！\n");
            break;
        default:
            printf(" I'm sorry ,  Fail to meet the reward conditions or exceed the length of service ！！\n");
            break;
            }
        break;    
    }
    return 0;
}