seperate the word from a sentence without library function - c

Question

Here i wrote a code to separate the words from a given sentence without using strtok() function.But the problem is it only prints the first word.Why rest of the words don't get printed ?
#include <stdio.h>
#include <string.h>
int main ()
{
char str[] ="This, a sample string.";
int i=0,k,begin,end;
while(str[i]!='\0'){
while(str[i]==' '){
i++;
}
begin = i;
while(str[i]!=' ' && str[i]!='\0'){
i++;
}
end = i-1;
char *ptr =(char *)malloc((end-begin)*sizeof(char));
for(k=begin;k<=end;k++){
ptr[k] = str[k];
}
printf("%s\n",ptr);
if(str[i]=='\0'){
break;
}
}
}

Answer 1

The complete code should be like this.
I have changed code on top of your code.
int main ()
{
char str[] ="This, a sample string.";
int i=0,k,begin,end;
int t;
while(str[i]!='\0'){
begin = i;
while(str[i]!=' ' && str[i]!='\0'){
i++;
}
end = i-1;
char *ptr = (char *) malloc( (i-begin)*sizeof(char) + 1);
t=0;
for(k=begin;k<=end;k++){
ptr[t++] = str[k];
}
ptr[t] = '\0';
puts(ptr);
if(str[i]=='\0'){
break;
} else
while(str[i] == ' ') i++; //To avoid multiple spaces
}
return 0;
}
-Thanks

Answer 2

The problem with your code is here:
for(k=begin;k<=end;k++){
ptr[k] = str[k];
}
the k is being used as index variable for both ptr and str, what you should do is use a separate variable for ptr, so that it fills up characters from 0 index.
Also you are not allocating the correct amount of space. The number of characters are end - begin + 1 and you also have to allocate space for null character(string terminating character).
So correct allocation is:
char *ptr =(char *)malloc((end-begin+2)*sizeof(char));
and your correct code is:
int index = 0;
for(k = begin;k <= end; k++){
ptr[jj++] = str[k];
}
ptr[end - begin + 1] = '\0';

Answer 3

If you're allowed to modify the string in-place, you could do something like
#include <stdio.h>
static void print_words(char *str) {
char *start = str; // Word start pointer.
for(;*str;str++) { // While there are characters...
if(*str == ' ') { // Space found!
*str = '\0'; // Replace the space with a null to end the string
printf("%s\n", start); // Output the now null-delimited string
*str = ' '; // Return the string to its original form
start = str + 1; // Advance the word-start pointer
}
}
printf("%s\n", start); // Print the last word remaining unprinted, if any
}
int main()
{
char str[] = "This, a sample string.";
print_words(str);
}

Answer 4

You have missed some logics in your code.
you are traversing to second word by default. Which is not your requirement.
This block identifies word from given string.
You are allocation one byte less than we need.
One extra byte is required for termination string. null char.
**4. ptr[k] = str[k]
This is the hole in your code.
This should be like ptr[0] = str[k];**
you missed incrementing i value to iterate further.
==================point 1=======================
while(str[i]!='\0'){
while(str[i]==' '){ -> this is point no 1. This logic will skip first word
i++;
}
=================point 2 ================
begin = i;
while(str[i]!=' ' && str[i]!='\0'){
i++;
}
**end = i-1;**
==========================================
char *ptr =(char *)malloc((end-begin)*sizeof(char)); -> point 3.
point 4 :
for(k=begin;k<=end;k++){
ptr[k] = str[k];
}
printf("%s\n",ptr);
if(str[i]=='\0'){
break;
}
point 5 :
else
i++;
}
-Thanks

Answer 5

I have found the problem and come up with the solution :
1.First problem is i was not assigning the correct value to *ptr.so , i used a variable j to start from the beginning of current index
2.I needed to null terminate each capture
ptr[k]='\0';
3.So the changes i made overall is the following :
for(k=0,j=begin;k<=end-begin;k++,j++){ // use a variable j to start from the beginning of current index
ptr[k] = str[j];
}
ptr[k]='\0';
Full code:
#include <stdio.h>
#include <string.h>
int main ()
{
char str[] ="This, an sample string.";
int i=0,j,k,begin,end;
char *ptr;
while(str[i]!='\0'){
while(str[i]==' '){
i++;
}
begin = i;
while(str[i]!=' ' && str[i]!='\0'){
i++;
}
end = i-1;
ptr =(char *)malloc((end-begin)*sizeof(char));
for(k=0,j=begin;k<=end-begin;k++,j++){ // use a variable j to start from the beginning of current index
ptr[k] = str[j];
}
ptr[k]='\0';
printf("%s\n",ptr);
if(str[i]=='\0'){
break;
}
}
}