C Pen question (1)

the difference between 1.sizeof and strlen

#include <stdio.h>

#include <string.h>

int main ()

{

Char a[10] = "12345";

Char *p = "12345";

Char b[20];

printf ("%d%d\n", sizeof (a), strlen (a));

/*sizeof is an operator,strlen is a function,andsizeof wants to add '/0 ',

Strlen represents the length of the string, and the strlen parameter can only be ' char* ' * /

printf ("%d%d\n", sizeof (*a), strlen (a));

printf ("%d%d\n", sizeof (p), strlen (p));

printf ("%d%d\n", sizeof (*P), strlen (p));

/* because b is unknown, so strlen is uncertain * /

printf ("%d%d\n", sizeof (b), strlen (b));

printf ("%d%d\n", sizeof (*B), strlen (b));

return 0;

}

Operation Result:

10 5

1 5

4 5

1 5

20 23

1 23

2. Running results of the following programs

#include <stdio.h>

int main ()

{

Double a[2]={3,9},*p,*q;

p=&a[0];

q=p+1;

printf ("%d%d\n", (q-p), (int) q (int) p);

return 0;

}

Run Result:1 8

3. The following procedures

#include <stdio.h>

int main ()

{

#define SUN 0

printf ("1");

#ifndef SUN

printf ("2");

#endif

printf ("3");

return 0;

}

Operation Result:

13

4. When the arrayint *p= (int*) malloc (10*sizeof (int))at the time of releaseFree (p), this is because the compilermallocsome special processing is done to ensure that the memory can be freed correctly. And whenint *p=new int[10]the release should beDelete []p, note[]the function of the description is to release an array of memory ifDelete Pit's just released.P[0], the remaining9aintthe memory is not released because it is specified as[], the compiler actually does a loop to release all the memory for this array.

5. Find out1~13in the integer1Number of occurrences,and figure out100~1300in the integer1The number of occurrences? For that, he counted a few.1~13included in1the number has1,Ten, One, A, -so there is a total6Times,But he has no problem with the latter. AcmerI hope you 'll help him.,and to make things more universal.,can quickly find out any non-negative integer range1the number of occurrences.

int numberof1between1andn_solution (int n)

{

int count=0;

for (int j=1;j<=n;j++)

{

int i=j;

while (i)

{

if (i%10==1)

count++;

I=I/10;

}

}

return count;

}

6. For statements such as a= (b++,c++), the value of a is C + +.

The header file of the 7.fork () function is #include<unistd.h>, and the fork () function is incremented by 2 of the n-th.

C Pen question (1)