Thread: Transposing Data HELP!!!

I'm a college student learning how to program in C. We recently got an assignment to transpose a list of names. We have to read in from a file a list of names and print them out and write to a file with the names going downwards.

I'm not asking for anyone to do my homework so please don't tell me that you won't because I know that. I simply need some pointers.

I'm going to use a 2 dimensional array as well as a double for loop for the printing.

Does anyone have any pointers on how to do this?

Code:

#include <string.h>
#include <stdio.h>
 
char transpose_text(char names[20][60])
{
    int i, j;
    for (i=0;i<17;i++)
         for(j=0;j<60;j++)
             printf("%s", names[i][j]);
 
 
}
 
void main (void)
{
     FILE *pnames, *trans;
     char names[20][60];
     int i; /* first for loop variable */
     int j; /* second for loop variable */
 
     pnames = fopen(file directory, "r");
     trans = fopen(file directory, "w");
 
     while (fscanf (pnames, "%d", &trans) != EOF)
     {
          fgets(names, 60, pnames);
          printf("%s", names);
          fprintf(trans, "%s \n", names);
     }
 
     transpose_text(names[20][60]);
 
     getche();
}

I currently have this but it doesn't transpose the names yet. I'm working on that. Any help?

What do you mean by transpose exactly? The letters? By how much?

If you mean transposing the characters by a predefined value, then you can take advantage of the fact that ascii letters have a numeric representation. i.e adding 1 to 'a' gives 'b' and so on. Not all ascii characters are printable though, so you need to figure out how to handle that, and decide if it matters.

I mean transposing like rows to columns. In other words, we have to print the names not in rows but in columns.

Then you should probably switch your loops, that is, for each j print all i's.

On line 9 I already tried switching the i with j and vice versa but the program crashes shortly after that.

You can't just switch i and j since you do not have 60 rows. I don't know what you are doing in line 24 btw, both pname and trans are file pointers.

Compile with your warnings turned all the way up. Here's what I get when I compile your program:

Code:

$ gcc -Wall -g -std=c99  transpose.c   -o transpose
transpose.c: In function ‘transpose_text’:
transpose.c:8: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘int’
transpose.c: At top level:
transpose.c:10: warning: return type of ‘main’ is not ‘int’
transpose.c: In function ‘main’:
transpose.c:16: error: ‘file’ undeclared (first use in this function)
transpose.c:16: error: (Each undeclared identifier is reported only once
transpose.c:16: error: for each function it appears in.)
transpose.c:16: error: expected ‘)’ before ‘directory’
transpose.c:16: error: too few arguments to function ‘fopen’
transpose.c:17: error: expected ‘)’ before ‘directory’
transpose.c:17: error: too few arguments to function ‘fopen’
transpose.c:18: warning: format ‘%d’ expects type ‘int *’, but argument 3 has type ‘struct FILE **’
transpose.c:20: warning: passing argument 1 of ‘fgets’ from incompatible pointer type
/usr/include/stdio.h:604: note: expected ‘char * restrict’ but argument is of type ‘char (*)[60]’
transpose.c:21: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘char (*)[60]’
transpose.c:22: warning: format ‘%s’ expects type ‘char *’, but argument 3 has type ‘char (*)[60]’
transpose.c:24: warning: passing argument 1 of ‘transpose_text’ makes pointer from integer without a cast
transpose.c:3: note: expected ‘char (*)[60]’ but argument is of type ‘char’
transpose.c:25: warning: implicit declaration of function ‘getche’
transpose.c:15: warning: unused variable ‘j’
transpose.c:14: warning: unused variable ‘i’
make: *** [transpose] Error 1

To clean this up:

• Line 8: %s is for whole strings, i.e. char *. You're using names[j][i] which is just a char. Read the printf docs, you want %c.
• Line 10: It's int main(void) and return an int at the end, usually 0. Read this: FAQ > main() / void main() / int main() / int main(void) / int main(int argc, char *argv[]) - Cprogramming.com.
• Line 16-17: Read up on how to use fopen. Also, check the return value and if fopen failed, print an error (look into perror) and exit your program immediately.
• Line 18: Read some examples on scanf. You need an int variable to store a %d result from scanf. Make sure to pass the address of that int to scanf.
• Line 20: names is effectively a char **. You just want a char *, so use a counter variable, say i, to count how many names so far. Then do something like fscanf(names[i], sizeof(names[i]), pnames);. The sizeof trick allows you to avoid magic numbers, so you can change the maximum name length in one place only.
• Line 21-22: Again, use a counter variable i and print names[i].
• Line 24: names[20][60] doesn't pass the whole array. It tries to pass the 61st "column" of the 21st "row", but you only have 20 rows and 60 columns. Remember, arrays in C start at 0 and end at size-1. Just pass 'names' without the [ ].
• Line 25: getche is not a standard function. Try getchar instead.
• Line 14-15: remove any variables you don't need
• Why does your transpose function stop at 17 instead of 20? This is another good reason to avoid magic numbers and use a constant.
• After you transpose your array, you have to remember that the null characters that end a name are in each column. It might help if you set the entire names array to all null characters, and in your transpose function, simply print nothing or a space for null characters.