Kernighan and Ritchie - exercise 3.3 (expand function) - c

Question

I have solved the exercises 3.3 from the K&R book. The solution I have implemented seems to work, but is a bit verbose and there could be smarter way to write this code. I wanted to ask if there could be problems with the solution I implemented and if there were easier way to write it:
Write a function expand(s1,s2) that expands shorthand notations like
a-z in the string s1 into the equivalent complete list abc...xyz in
s2. Allow for letters of either case and digits, and be prepared to
handle cases like a-b-c and a-z0-9 and -a-z. Arrange that a leading or
trailing - is taken literally
My code is this one:
#include <stdio.h>
void expand(char s1[],char s2[]){
int j=0,i=0;
while(s1[j] != '\0'){
if (s1[j]>= 'a' && s1[j] <= 'z' && s1[j+1] == '-' && s1[j+1]!='\0' && s1[j+2] >= 'a' && s1[j+2] <= 'z' && s1[j+2] !='\0'){
int z = s1[j+2]-s1[j];
int c;
for (c=0;c<=z;c++){
s2[i]= c+s1[j];
i++;
}
j=j+3;
}
else if (s1[j]>= 'A' && s1[j] <= 'Z' && s1[j+1] == '-' && s1[j+1]!='\0' && s1[j+2] >= 'A' && s1[j+2] <= 'Z' && s1[j+2] !='\0'){
int z = s1[j+2]-s1[j];
int c;
for (c=0;c<=z;c++){
s2[i]= c+s1[j];
i++;
}
j=j+3;
}
else if (s1[j]>= '0' && s1[j] <= '9' && s1[j+1] == '-' && s1[j+1]!='\0' && s1[j+2] >= '0' && s1[j+2] <= '9' && s1[j+2] !='\0'){
int z = s1[j+2]-s1[j];
int c;
for (c=0;c<=z;c++){
s2[i]= c+s1[j];
i++;
}
j=j+3;
}
else if (j!= 0 && s1[j] == '-' && (s1[j-1] < s1[j+1])){
int z = s1[j+1]-(1+s1[j-1]);
int c;
for (c=0;c<=z;c++){
s2[i]= c+(s1[j-1]+1);
i++;
}
j=j+2;
}
else if ( s1[j]>= 32 && s1[j] <= 127 && (s1[j+1] != '-' || s1[j+1]>= 32 && s1[j+1] <= 127 )){
s2[i] = s1[j];
j++;
i++;
}
}
s2[i]='\n';
i++;
s2[i]='\0';
}
int main() {
int c;
char s2[100];
expand("-a-c,a-c-g,A-Z0-9--", s2);
printf("%s",s2);
}
The code works in this way:
First it check if there is a triplet of the kind "x-y" where x<y. Then if gives to the array the values from x to y included and jump to the next character after the triplet "x-y". The same is done for upper case letters and for numbers in further if conditions.
the condition else if (j!= 0 && s1[j] == '-' && (s1[j-1] < s1[j+1])) is used to check for cases like "a-c-d1". The code I have implemented in this example will work like this:
Since we start with the 0-th character in "a-c-d" and the pattern "x-y" is present, "abc" will be assigned to the array. then we will directly jump to the second - in "a-c-f". Since this second - is preceded by a letter "c" and followed by a letter "f", and "c"<"f", then the characters between "c" and "f" will be assigned to the array, excluding the initial "c". Then the index for the string will jump of two and reach 1.

Answer 1

Some other way :
you only to know the last char before - and if it is the same type as current one (lower or upper case letter or digit)
when you get a - and previous char is a letter or digit you know you may have to make expansion
if you have a letter or digit after - and it is corresponding to letter/digit before - you know you can expand from char before / to current one.
you do need to look forward but only save previous char and char before -
you do same kind of processing for each different char type (letter/digit)
You can find an example after :
#include <stdio.h>
// handle different char type
typedef enum E_chartype {
LowerCaseLetter,
UpperCaseLetter,
Digit09,
OtherChar
} E_chartype;
// save if we may have a posdible expansion
typedef enum E_states {
NothingStarted,
StartedExpansion
} E_states;
// find type of a char
E_chartype getCharType(char c) {
if ((c >= 'a') && (c <= 'z'))
return LowerCaseLetter;
if (( c >= 'A') && (c <= 'Z'))
return UpperCaseLetter;
if ((c >= '0') && (c <= '9'))
return Digit09;
return OtherChar;
}
void expandopt(char *inS, char *outS) {
// init output string to null string
outS[0] = 0;
char *endS = outS;
E_states automat = NothingStarted;
char savedChar = 0;
int currentIndex;
E_chartype prevCType=OtherChar,savedCType=OtherChar;
char savedC = 0,prevC=0;
// loop on input string
for (currentIndex = 0; inS[currentIndex] != 0;currentIndex++) {
// save current char in variable c for shorter writting
char c = inS[currentIndex];
printf("%c : ",c);
// save type of current char
E_chartype currentCType = getCharType(c);
switch (automat) {
// genersl case notjing yet started
case NothingStarted:
// possibkee expansion if previous chsr is letter or digit and current char is -
if ((prevCType != OtherChar) && (c == '-')) {
printf("start rep\n");
automat = StartedExpansion;
// save the previous char and its type as it eill br the reference fircexpansion
savedCType = prevCType;
savedC = prevC;
} else {
// reset and cooy current char to iutput
automat = NothingStarted;
printf("nothing\n");
*endS++ = c;
}
break;
case StartedExpansion:
// we make ecpansion only if still same char type and letter/digit is strictly after saved one
if ((currentCType == savedCType) && (c > savedC)){
printf("expansion ");
for (char newC
= savedC+1;newC <= c;newC++) {
*endS++ = newC;
}
// save char in case thrre id a - after, which mean nee expansion
savedC = c;
} else {
// save current chsrcsnd its type
savedCType = currentCType;
savedC = c;
// copy previous char (= -) whch was not vopief in case of expansion
*endS++ = prevC;
*endS++ = c;
}
automat = NothingStarted;
break;
}
// save current chsr and type
prevCType = currentCType;
prevC = c;
}
// add 0 at end of string
*endS = 0;
}
int main() {
expandopt("-a-c,a-c-g,A-Z0-9–",s2);
printf("%s\n",s2);
}
Sorry for the code formatting, I did not find good code editor on phone.