Thread: homework help!!

I need to change this program into pointer arithmetic

I started doing it and I just want to make sure that I have not left out someting!!!!!!



#include <stdio.h>

int main(void)
{
char t[20];
char buf[20];
char *pt;
int k;

for(;
{
gets(t);
if (feof(stdin))break;
sscanf(t,"%s", &buf);

pt=t;
while(strlen(pt)-1; k>=0; k--)
{
printf("%c", *pt[k]);
}
printf("\n");
}
return 0;
}

Let's see.

1. #include <string.h> isn't there.
2. for(; << what do want to do with this?
3. if (feof(stdin)) I don't think you meant that.
4. sscanf(t,"%s", &buf); is unnecessary.
5. while(strlen(pt)-1; k>=0; k--) makes no sense
6. printf("%c", *pt[k]); makes no sense

1. Add #include <string.h>
2. Complete the for loop
3. if (feof(stdin)) Rather do if(t[0] == '\n')
4. while(strlen(pt)-1; k>=0; k--) Do this : while(*(pt++) != '\0')
5. printf("%c", *pt[k]); change to "printf("%c", *pt);"

sorry here is my updated codes

Why do I need string.h?

if (feof(stdin)) break; I need that to stop the program from its endless loop.

This program prints a string backward


#include <stdio.h>

int main(void)
{
char t[20];
char buf[20];
char *pt;
int k;


for(;
{
gets(t);
if (feof(stdin))break;
sscanf(t,"%s", &buf);

pt=t;
while(strlen(pt)-1; k>=0; k--)
{
printf("%c", *pt[k]);
}
printf("\n");
}
return 0;
}

>Why do I need string.h?

It's required for the string-functions you are using.

>if (feof(stdin)) break; I need that to stop the program from its
>endless loop.

Not necessarily. More elegant would be to have an if-else construction and a variable which indicates if the loop should end.

Code:

while (... && stop == FALSE)
{
    if (feof (stdin))
    {
        stop = TRUE;
    }
    else
    {
        ...
    }
}

>while(strlen(pt)-1; k>=0; k--)

Hmmm. I suggest you read you're C book again and especially the chapters about while-loops and for-loops.

sorry this is a for loop not a while loop

I see. Still any questions?

how can i change the for loop into pointer arithmetic??

You mean this while-loop which is in fact a for-loop?

>while(strlen(pt)-1; k>=0; k--)

Could be something like this. (Not tested)

Code:

/*First store length of t in a variable. */
t_len = strlen (t) - 1;

/* Let pt point to end of t and then move backwards. Loop ends when start of t is reached. */
for (pt = t + t_len; pt >= t; pt--)
{
    ...
    printf ("%c", *pt);
    ...
}

Thanks shiro!