一个很莱的C程序

devel

请帮忙，这么简单的我都不懂。都不好意思问了。
# gcc -c twof2.c
twof2.c: In function `main':
twof2.c:3: warning: initialization from incompatible pointer type
# cat twof2.c
main()
{
int a[2][3],*p=a;
int i,j;
for(i=0;i<2;i++)
for(j=0;j<3;j++)
  scanf("%d",p+i*3+j);
for(i=0;i<2;i++)
  {
     printf("\n");
     for(j=0;j<3;j++)
      printf("%10d",*(p+i*3+j));
  }
}

#

libinary

只是个警告，因为a是int [2][3]，编译器告诉你这里可能有问题，如果你知道自己确实要这么做就没有问题，可以不理它。
从你的程序来看没什么问题，不过你既然都用了两个循环，干脆用a[j]算了，比指针好看多了

devel

谢谢版主，但学到指针，要做些练习的。
顺便问一下，指针的真正作用是节省内存吗？

xuyunsong

不全是，还提高速度和增强功能

藍天

I am also learning C, and I am not a professional.  The following is one of the homework for last week.   It may help a bit on how pointer works.
This program check a list of word from a file for palindromes (正讀反讀都一樣的詞).
Pointers are very useful when pass data in between functions.
Also give me some comment please.

1. 
   
2. #include <stdio.h>
   
3. 
   
4. int readFile(char *, char **);
   
5. void palindromeCheck(char *);
   
6. 
   
7. int main (void)
   
8. {
   
9.     char *palindromeList, filename[255] = {'\0'};
   
10. 
    
11.     /* ask user for the filename */
    
12.     printf("\nPlease enter the filename of your Palindrome list.\n"
    
13.            ": ");
    
14.     scanf("%s", filename);
    
15. 
    
16.     /* read the word list into memory */
    
17.     if (readFile(filename, &palindromeList))
    
18.        exit(1);
    
19.     putc('\n', stdout);
    
20. 
    
21.     /* chck each word for palindrome */
    
22.     palindromeCheck(palindromeList);
    
23.    
    
24.     return 0;
    
25. }
    
26. 
    
27. void palindromeCheck(char *buffer)
    
28. {
    
29.      int palindrome;
    
30.      char *firstChr, *lastChr, *endLine;
    
31. 
    
32.      firstChr = endLine = buffer;
    
33. 
    
34.      /* loop until end of file */
    
35.      while (*firstChr != EOF)
    
36.            {
    
37.            palindrome = 1;
    
38.            /* find the last character */
    
39.            while (*endLine != '\n')
    
40.                  putc(*(endLine++), stdout);
    
41.            lastChr = endLine - 1;
    
42.            /* palindrome compair */
    
43.            while ( (firstChr != lastChr) && ((firstChr + 1) != lastChr) )
    
44.                  if (*(firstChr++) != *(lastChr--))
    
45.                     palindrome = 0;
    
46.            firstChr = ++endLine;
    
47. 
    
48.            /* display result */
    
49.            printf(" %s a palindrome\n", (palindrome)? "is":"is not");
    
50.            }
    
51. }
    
52. 
    
53. int readFile(char *filename, char **buffer)
    
54. {
    
55.     unsigned int count = 0;
    
56.     FILE *fptr;
    
57.    
    
58.     if ( (fptr = fopen(filename, "r")) == NULL )
    
59.        {
    
60.        fprintf(stderr, "Error Openning Source Code File %s!\n", filename);
    
61.        return 1;
    
62.        }
    
63.    
    
64.        /* get the size of the file for memory allocation.
    
65.         * read the file onec and count the character make
    
66.         * the code protable.*/
    
67.         while (getc(fptr) != EOF)
    
68.               count++;
    
69.         rewind(fptr);
    
70. 
    
71.        /* allocate memory */
    
72.        *buffer = malloc(count * sizeof(char));
    
73. 
    
74.        /* read in the word list and echo them to stdout */
    
75.        puts("\nReading Palindrome List From File:");
    
76.        count = 0;
    
77.        while ( (*(*buffer + count) = getc(fptr)) != EOF)
    
78.               putc(*(*buffer + count++), stdout);
    
79.       
    
80.        fclose(fptr);
    
81.        return 0;
    
82. }
    

复制代码

Data File "test.dat"

1. 
   
2. anna
   
3. pip
   
4. +-*-+
   
5. world
   
6. sky
   
7. same
   
8. ga1ag
   

复制代码

Run Log:
Please enter the filename of your Palindrome list.
: test.dat
                                                                              
Reading Palindrome List From File:
anna
pip
+-*-+
world
sky
same
ga1ag
                                                                              
anna is a palindrome
pip is a palindrome
+-*-+ is a palindrome
world is not a palindrome
sky is not a palindrome
same is not a palindrome
ga1ag is a palindrome