Programmer --- C language details 26 (Boolean Type in C language, continue details, sizeof example, strlen example), --- cstrlen

Programmer --- C language details 26 (Boolean Type in C language, continue details, sizeof example, strlen example), --- cstrlen
Main Content: boolean type, continue details in C language, sizeof example, strlen example
I. boolean type

Many people may not know that the C language already has the Boolean Type: Starting from the C99 standard, the type name is "_ Bool"

Before the C99 standard, we often mimic and define the boolean type. There are several common methods:

1. method 1

#define TURE 1#define FALSE 0

2. method 2

typedef enum {false, true} bool;

3. Method 3

typedef int bool

Idle int is a waste of memory and is used by memory-sensitive programs.

typedef char bool

The header file added in the C99 standard introduces the bool type, which is compatible with the bool type in C ++. The header file is stdbool. h, and its source code is as follows:

#ifndef _STDBOOL_H #define _STDBOOL_H  #ifndef __cplusplus  #define bool    _Bool #define true    1 #define false   0  #else /* __cplusplus */  /* Supporting <stdbool.h> in C++ is a GCC extension.  */ #define _Bool   bool #define bool    bool #define false   false #define true    true  #endif /* __cplusplus */  /* Signal that all the definitions are present.  */ #define __bool_true_false_are_defined 1#endif /* stdbool.h */ 

Ii. continue

The detail of continue is used in the loop. Otherwise, an error is reported.

# Include <stdio. h> int main () {int a = 1; switch (a) {case 1: printf ("1 \ n"); continue; // continue must be used in the break loop; case 2: printf ("2 \ n"); default: break;} return 0 ;}

Iii. sizeof example

# Include <stdio. h> int B [100]; void fun (int B [100]) {printf ("in fun sizeof (B) = % d \ n", sizeof (B )); // int main () {char * p = NULL; printf ("sizeof (p) = % d \ n ", sizeof (p); printf ("sizeof (* p) = % d \ n", sizeof (* p); printf ("--------------------- \ n "); char a [100]; printf ("sizeof (a) = % d \ n", sizeof (a); printf ("sizeof (a [100]) = % d \ n ", sizeof (a [100]); printf (" sizeof (& a) = % d \ n ", sizeof (& )); printf ("sizeof (& a [0]) = % d \ n", sizeof (& a [0]); printf ("--------------------- \ n "); fun (B); return 0 ;}

Output:

Iv. Example of strlen

# Include <stdio. h> # include <stdlib. h> # include <string. h> # include <stdbool. h>/* Question 1: how to store-0 and + 0 in the memory? 2. int I =-20; unsigned j = 10; what is the value of I + j? Why? 3. What is the problem with the following code? Unsigned I; for (I = 9; I> = 0; I --) {printf ("% u \ n", I) ;}*/int main () {bool bool2 = 0;/* C bool type is available only in C99, if it does not contain the header file stdbool. h. If you use bool directly, an error will be reported */_ Bool bool1 = 1;/* You can directly use _ Bool instead of stdbool. h */char a [280]; char * str = "12340987 \ 0 56"; char test [] = "12340987 56"; int I; printf ("strlen () = % d \ n ", strlen (a); for (I = 0; I <280; I ++) {a [I] =-1-i; // a [1, 256] = 0 // printf ("a [% d] = % d \ n", I, a [I]);} printf ("strlen (a) = % d \ n", strlen (a); // Why is it 255 printf ("strlen (str) = % d \ n ", strlen (str); printf ("strlen (test) = % d \ n", strlen (test); char s = '\ 0 '; printf ("\ 0 = % d \ n", s); return 0 ;}

Output: