Programmer --- C language details 26 (boolean type, continue details in C language, sizeof example, strlen example)

Programmer --- C language details 26 (boolean type, continue details in C language, sizeof example, strlen example)
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  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

int main ()
{
int a = 1;
switch (a)
{
case 1:
printf ("1 \ n");
continue; // continue must be used in a loop
break;
case 2:
printf ("2 \ n");
default:
break;
}
return 0;
}
 

Iii. sizeof example

#include
int b [100];
void fun (int b [100])
{
printf ("in fun sizeof (b) =% d \ n", sizeof (b)); // I feel that the array in the function is processed as a pointer
}
int main ()
{
char * p = NULL;
printf ("sizeof (p) =% d \ n", sizeof (p));
printf ("sizeof (* p) =% d \ n", sizeof (* p));
Ranch
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 (& a));
printf ("sizeof (& a [0]) =% d \ n", sizeof (& a [0]));
printf ("----------------------- \ n");
fun (b);
return 0;
}

Output:

Iv. Example of strlen

#include
#include
#include
#include
/ *
Problem
How are -0 and +0 stored in memory?
2.int i = -20;
unsigned j = 10;
What is the value of i + j? why?
3. What's wrong with the following code?
unsigned i;
for (i = 9; i> = 0; i--)
{
printf ("% u \ n", i);
}
* /
int main ()
{
bool bool2 = 0; / * C language bool type is only available in C99, if the header file stdbool.h is not included, using bool directly will report an error * /
_Bool bool1 = 1; / * Use _Bool directly without including stdbool.h * /
char a [280];
char * str = "12340987 \ 0 56";
char test [] = "12340987 56";
int i;
printf ("strlen (a) =% d \ n", strlen (a));
for (i = 0; i <280; i ++)
{
a [i] = -1-i; // a [256] = 0
// printf ("a [% d] =% d \ n", i, a [i]);
}

printf ("strlen (a) =% d \ n", strlen (a)); // why is 255
printf ("strlen (str) =% d \ n", strlen (str));
printf ("strlen (test) =% d \ n", strlen (test));
Ranch
char s = '\ 0';
printf ("\\ 0 =% d \ n", s);
return 0;
} 
  
  
 

Output: