code which reverses a string of characters....just need some feed back.........

C

Ceriousmall

I'm just putting this out to get some general feed
back..........................

/* 2011 Ceriousmall
This piece of code reverses the character string using the
function reverse(s) */

#include <stdio.h>

#define MAXLINE 1000 /* maximum input line size */

/* assigns the character string to ln[] */
int gotline(char ln[])
{
int c, i;
int at_end;

for (i = 0; i < MAXLINE-1 && (c = getchar()) != EOF && c != '\n'; +
+i)
ln = c;
at_end = c == EOF;

if (c == '\n') {
ln = c;
++i;
}
ln = '\0';

if (at_end)
return EOF;
else
return i;
}

/* reverses the character string s[] */
void reverse(char s[])
{
int i, x;
char subline[MAXLINE];

for (x = 0; s[x] != '\0'; ++x)
if (s[x] == '\n') {
i = x;
--i;
}
else
i = x;

for (x = 0; i >= 0; ++x && --i) {
subline[x] = s;
subline = s[x];
}
for (i = 0; i < x; ++i)
s = subline;
}

int main(void)
{
int return_val;
int at_start, at_end;
char line[MAXLINE];

at_start = 0;

while (at_start != EOF) {
return_val = gotline(line);
at_end = return_val == EOF;
reverse(line);
printf("\n%s", line);
putchar('\n');

if (at_end)
at_start = EOF;
}
return 0;
}

I've also found a better way to do the flip on the text stream in
reverse[] but its not
entirely my own idea but i was heading in that general direction,
this was just the nudge i needed.

/* reverses the character string s[] */
void reverse(char s[])
{
int i, x;
char chr;

for (x = 0; s[x] != '\0'; ++x)
if (s[x] == '\n') {
i = x;
--i;
}
else
i = x;

for (x = 0; x < i; ++x && --i) {
chr = s[x];
s[x] = s;
s = chr;
}
}
 
A

August Karlstrom

I'm just putting this out to get some general feed
back..........................

/* 2011 Ceriousmall
This piece of code reverses the character string using the
function reverse(s) */

#include<stdio.h>
Click to expand...

[...]

Note that there is a much shorter (but slower) solution using recursion:

#include <stdio.h>

void reverse(void)
{
int ch;

ch = getchar();
if (ch != '\n') {
reverse();
putchar(ch);
}
}


int main(void)
{
int ch;

ch = getchar();
while (ch != EOF) {
ungetc(ch, stdin);
reverse();
putchar('\n');
ch = getchar();
}
return 0;
}


/August
 
A

August Karlstrom

On 2011-03-28 13:24, August Karlstrom wrote:
[...]
#include <stdio.h>

void reverse(void)
{
int ch;

ch = getchar();
if (ch != '\n') {
Click to expand...

We may want to replace the last line above with

if ((ch != EOF) && (ch != '\n')) {

in order to handle files without newline ending.


/August
 
B

Ben Bacarisse

Ceriousmall said:
I'm just putting this out to get some general feed
back..........................

/* 2011 Ceriousmall
This piece of code reverses the character string using the
function reverse(s) */

#include <stdio.h>

#define MAXLINE 1000 /* maximum input line size */

/* assigns the character string to ln[] */
int gotline(char ln[])
Click to expand...


It's much more useful to have a function that can be told how long the
array is with a second parameter.
{
int c, i;
int at_end;

for (i = 0; i < MAXLINE-1 && (c = getchar()) != EOF && c != '\n'; +
+i)
ln = c;
at_end = c == EOF;

if (c == '\n') {
ln = c;
++i;
}
ln = '\0';

if (at_end)
return EOF;
else
return i;
Click to expand...


The use of at_end seems a little over the top. You could eliminate it
altogether and just end the function with

return c == EOF ? EOF : i;
}

/* reverses the character string s[] */
Click to expand...

This does not do what is says. A reader used to C will expect that all
the character are reversed, but you specifically exclude a terminating
newline.
void reverse(char s[])
{
int i, x;
char subline[MAXLINE];

for (x = 0; s[x] != '\0'; ++x)
if (s[x] == '\n') {
i = x;
--i;
Click to expand...

i = x - 1;
}
else
i = x;
Click to expand...

There's no need to set i every time. In fact you should be using
strlen.
for (x = 0; i >= 0; ++x && --i) {
Click to expand...

Its clearer to write ++x, --i rather than use &&.
subline[x] = s;
subline = s[x];
}
for (i = 0; i < x; ++i)
s = subline;
}

int main(void)
{
int return_val;
int at_start, at_end;
char line[MAXLINE];

at_start = 0;

while (at_start != EOF) {
return_val = gotline(line);
at_end = return_val == EOF;
reverse(line);
printf("\n%s", line);
putchar('\n');

if (at_end)
at_start = EOF;
}
return 0;
}
Click to expand...


Again, rather too any extra variables for my taste and it's a shame that
the length of the string (which you know form gotline) is not used --
you end up re-scannign it in the reverse function.

<snip>
 
C

Ceriousmall

Thanks for the feed back guys............. I even missed a few
elementary things.............
 
L

Lew Pitcher

I'm just putting this out to get some general feed
back..........................

/* 2011 Ceriousmall
This piece of code reverses the character string using the
function reverse(s) */

#include <stdio.h>

#define MAXLINE 1000 /* maximum input line size */

/* assigns the character string to ln[] */
int gotline(char ln[])
{
int c, i;
int at_end;

for (i = 0; i < MAXLINE-1 && (c = getchar()) != EOF && c != '\n'; +
+i)
ln = c;
at_end = c == EOF;

if (c == '\n') {
ln = c;
++i;
}
ln = '\0';

if (at_end)
return EOF;
else
return i;
}

/* reverses the character string s[] */
void reverse(char s[])
Click to expand...

[snip]

void reverse(char s[])
char *front, *back;

/* find the end of the string */
for (back = s; *back != 0; ++back) {/*nop*/}

/* swap front with back, move both toward middle */
for (front = s; front+1 < back; ++front, --back)
{
char temp;

temp = *(back-1);
*(back-1) = *front;
*front = temp;
}
}
 
L

Lew Pitcher

Oops.... copy&paste error

I'm just putting this out to get some general feed
back..........................

/* 2011 Ceriousmall
This piece of code reverses the character string using the
function reverse(s) */

#include <stdio.h>

#define MAXLINE 1000 /* maximum input line size */

/* assigns the character string to ln[] */
int gotline(char ln[])
{
int c, i;
int at_end;

for (i = 0; i < MAXLINE-1 && (c = getchar()) != EOF && c != '\n'; +
+i)
ln = c;
at_end = c == EOF;

if (c == '\n') {
ln = c;
++i;
}
ln = '\0';

if (at_end)
return EOF;
else
return i;
}

/* reverses the character string s[] */
void reverse(char s[])
Click to expand...

[snip]
Click to expand...


void reverse(char s[])
{
char *front, *back;

/* find the end of the string */
for (back = s; *back != 0; ++back) {/*nop*/}

/* swap front with back, move both toward middle */
for (front = s; front+1 < back; ++front, --back)
{
char temp;

temp = *(back-1);
*(back-1) = *front;
*front = temp;
}
}
 

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