Swap the 2nd character with the next-to-last - c

Question

I have to change the 2nd letter with penultimate letter for word with more than 3 letters.
Example i have this string: Alex are mere
The result should be: Aelx are mree
But i get this when i run my program: Axel` aler
This is the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
int i,n,j=0;
char text[81],cuv[44],l;
printf("Introduce-ti textul:");
gets(text);
for(i=0;i<strlen(text);i++)
{
if(text[i] != 32) {
cuv[j]=text[i];
j += 1;
} else {
n = strlen(cuv) - 1;
l= cuv[1];
cuv[1]=cuv[n-1];
cuv[n-1]=l;
printf("%s ",cuv);
strcpy(cuv,"");
j=0;
}
}
return 0;
}

Answer 1

First, you do not want to use gets. It was removed from the standard library because it was unsafe, use fgets instead. That being said, all you need to do is tokenize your input string into words, and then if the word is greater than 3 chars, swap the 2nd and next to last characters. One way would be:
#include <stdio.h>
#include <string.h>
#define MAXS 256
#define MAXW 64
int main (void) {
size_t len;
char str[MAXS] = {0};
char word[MAXW] = {0};
char *p = NULL;
fgets (str, MAXS, stdin); /* read input from stdin */
/* tokenize string */
for (p = strtok (str, " "); p; p = strtok (NULL, " \n"))
{
strncpy (word, p, MAXW - 1); /* copy token to word */
if ((len = strlen (word)) > 3) /* if word > 3 */
{
char tmp = word[1]; /* swap 2nd & next to last */
word[1] = word[len-2];
word[len-2] = tmp;
}
printf ("%s ", word);
}
putchar ('\n');
return 0;
}
Use/Output
$ printf "Alex are mere\n" | ./bin/swap2nd
Aelx are mree
or if you wanted to enter the text:
$ ./bin/swap2nd
Alex are mere
Aelx are mree
Second Method Using Start/End Pointers
You can also modify the original string ready be fgets in place by using nothing more than a start-pointer (p below) and end-pointer (ep below) to work your way down the string character-by-character, stopping each time the end-pointer points to a space, tab, or newline and then using the difference between the start and end pointers to check the length of the word and perform the character swap if the length is greater than 3 chars. You can work through each version and compare:
#include <stdio.h>
#define MAXS 256
int main (void) {
char str[MAXS] = {0};
char *p = NULL;
char *ep = NULL;
fgets (str, MAXS, stdin); /* read input from stdin */
p = ep = str;
while (*ep) /* for each char, if a space, tab or newline */
if (*ep == ' ' || *ep == '\t' || *ep == '\n') {
if ((ep - p) > 3) { /* if length > 3 */
char tmp = *(p + 1); /* swap chars */
*(p + 1) = *(ep - 2);
*(ep - 2) = tmp;
}
p = ++ep; /* set p to next word */
}
else
++ep;
printf ("%s\n", str);
return 0;
}
Use/Output
$ ./bin/swap2nd2
Alex are mere
Aelx are mree
Which approach you choose between these two methods, as well as the method posted by Vlad, is largely a matter of taste/choice. All are valid and are just different way of accomplishing the same thing. Let me know if you have questions.

Answer 2

Try the following approach
#include <stdio.h>
int main( void )
{
char s[] = "Alex Chiurtu";
char t[sizeof( s )];
size_t i = 0, j = 0;
do
{
t[i] = s[i];
if ( s[i] != ' ' && s[i] != '\t' && s[i] != '\0' )
{
++j;
}
else if ( j != 0 )
{
if ( j > 3 )
{
char c = t[i-j + 1];
t[i-j+1] = t[i-2];
t[i-2] = c;
}
j = 0;
}
} while ( s[i++] );
puts( s );
puts( t );
return 0;
}
The program output is
Alex Chiurtu
Aelx Ctiurhu
Take into account that function gets is unsafe and is not supported by the C Standard any more.
Also it is a bad idea to use magic numbers like 32. Its meaning is unclear.
In your program array cuv was not zero initialized therefore the following statement
n = strlen(cuv) - 1;
results in undefined behaviour of the program. Also it is not a good idea each time to calculate the length of the string.