How to reverse words one by one in c using pointers and arrays

Hey, yeah you guessed it homework. I am trying to print a string in reverse using pointers. Only the words though. So "hello world" is "olleh dlrow". What I'm doing in the code below is assigning one pointer(pSent开发者_如何学Pythonence, which is a string array of multiple words passed down from the main function) to a temporary pointer until a space, then increment backwards and print the character from the temporary pointer to the beginning of the word, then do it again. I'm currently stuck, I don't know how to mark the beginning of the word and increment only to that. I know the while(pt != '0') is not the way to do it at all. The prompt says to store the word into a temporary string(tmpStrg) and use pT to point to it, so maybe I need to do something with tmpStrg? Any help is much appreciated and thank you in advance!!

void prtWords(char *pSentence)
{
    char tmpStrg[81], *pT=tmpStrg;
    int length=0;

    while(*pSentence != '\0')
    {
       while(*pSentence != ' ' && *pSentence != '/0')
       {
         *pT=*pSentence;
         pT++;
         pSentence++;
         length++;
       }
       pSentence++;

       while(length >= 0);
       {
         printf("%c", *pT);
         pT--;
         length--;
       }
    }
}

void prtWords(char *pSentence)
{
    char tmpStrg[81], *pT=tmpStrg;

According to your code, I suppose here you use tmpStrg[81] as a new string for a word, and you print the word in reverse order later.

    int length=0;
    while(*pSentence != '\0')
    {
       while(*pSentence != ' ')
       {

Here is your problem for overflow, you should test \0 and at the same time (and change the second while to a && with first while unchanged). There is no guarantee that a sentence will end with a .

         *pT=*pSentence;
         pT++;
         pSentence++;
         length++;
       }
       pSentence++;
       while(length >= 0);

When length is 0, you should not do anything. Change to >.

       {
         printf("%c", *pT);

You should do pT-- first, because last pT++ does not have an assignment.

         pT--;
         length--;
       }

Here print a when *pSentence == ' '.

    }
}

Work out the full code yourself as it is homework. Any further questions are welcomed.

@Duck's comment "Break the problem into pieces." was spot on, and highlights one of the most important design/programming techniques.

I'm not familiar with what unit testing frameworks are most often used for testing C code, but another good place to start is write some tests.

This code may not be exactly what you are looking for, as it performs its work in place:

void ReverseInPlace(char * pstart, char * pend)
{
    char tmp;

    while (pend > pstart)
    {
        tmp = *pstart;
        *pstart++ = *pend;
        *pend-- = tmp;
    }
}

void ReverseWordsInPlace(char *pSentence) 
{
    char * pstart;
    char * pend; 
    pstart = pSentence;

    while (*pstart != '\0')
    {
        // skip any (multiple) starting spaces
        while (*pstart == ' ')
        {
            pstart++;
        }

        pend = pstart;

        // find end of word (terminated by a space or end of string)
        while (*pend != ' ' && *pend != '\0')
        {
            pend++;
        }

        // check if anything left to do
        if (pstart >= pend - 1)
            return;

        ReverseInPlace(pstart, pend - 1);

        pstart = pend;
    }
}

int main(int argc, char * argv[])
{

char string1[] = "The quick brown fox jumped over the lazy dog";
char string2[] = "_";
char string3[] = " ";
char string4[] = " another";
char string5[] = "hello ";  
char string6[] = "";
char string7[] = "  ab";

 ReverseWordsInPlace(string1);
 ReverseWordsInPlace(string2);
 ReverseWordsInPlace(string3);
 ReverseWordsInPlace(string4);
 ReverseWordsInPlace(string5);
 ReverseWordsInPlace(string6);
 ReverseWordsInPlace(string7);

printf("%s\n", string1);
printf("%s\n", string2);
printf("%s\n", string3);
printf("%s\n", string4);
printf("%s\n", string5);    
printf("%s\n", string6);
printf("%s\n", string7);

return 0; 
}