Thread: replace character with string

I need some help on writing code for the fill in the blank question type.

I would like the proccess to end with these results:
question:"C *"
answer:"Board"

question after * is replaced."C -----"

question:"Yet * question"
answer:"another"

question after * is replaced."Yet ------- question"

strtok and/or strchr are two functions that I'll probabley need, but that's all I know. Any hints?

You simply move to the end of the original string back up two, one for the \0 and the other for *. Then just write the rest of the string and terminate it.

Ok, I have made an attempt to use your advice to solve my problem.

Posted below is my code. What improvements I can make to it?

Code:

	 char input[80] = "January comes after * one two three.";
	 char input2[80] = "Feburary";
	 char replace[80];
	 char temp[80];
	 char *p;
	 int i = 0;
	 /* strtok places a NULL terminator
	 in front of the token, if found */
	 p = strtok(input, "*");
	 if (p)   printf("%s\n", p);
	 strcpy(temp,p);
	 for(i = 0;i < strlen(input2);i++)
		replace[i] = '_';
	 strcat(temp,replace);
	 printf("%s\n",replace);
	 /* A second call to strtok using a NULL
	 as the first parameter returns a pointer
	 to the character following the token  */
	 p = strtok(NULL, "*");
	 strcat(temp,p);
	 if (p)   printf("%s\n", p);
	 strcpy(input,temp);
	 printf("%s\n",input);

You are working with too many arrays of chars. I'd drop it down to to. Then just tidy up your code.

Sorry, but I don't see how you would use only two char arrays for that. Could you please explain?

>Sorry, but I don't see how you would use only two char arrays for that.

Yet another way.

Code:

#include <stdio.h>
#include <string.h>

char *foo(char *question, size_t size, const char *answer)
{
   size_t alen = strlen(answer);
   if ( alen + strlen(question) < size )
   {
      char *star = strchr(question, '*');
      if ( star != NULL )
      {
         memmove(star + alen, star + 1, strlen(star));
         memset(star, '-', alen);
         return question;
      }
   }
   return NULL;
}

int main()
{
   char question[80] = "The month before * is January.",  answer[] = "February";
   if ( foo(question, sizeof question, answer) != NULL )
   {
      puts(question);
   }
   return 0;
}

/* my output
The month before -------- is January.
*/

Thanks for the better solutions to this problem. I understand most of thefroggy's code, but I have problem with how memmove and memset work in Dave_Sinkula's solution. Could you tell me how they work in your in code?

>memmove(star + alen, star + 1, strlen(star));

void *memmove(void *dest, const void *src, size_t n);

The memmove() function copies n bytes from memory area src to memory area dest. The memory areas may overlap.

We have 'star' pointing to the asterisk. strlen(star) is the length of the remaining string, from the '*' up to, but not including, the '\0'. So the 'src' parameter is pointing to the character just after the '*'. And the value of 'alen' is the length of the answer string. Finally, 'dst' points to a location ahead of the '*' by 'alen', the length of the answer string.

So, we use memmove to copy the remaining string from the position after the asterisk to a position beyond the asterisk by the length of the answer string.

>memset(star, '-', alen);

void *memset (void *s, int c, size_t n);

The memset() function fills the first n bytes of the memory area pointed to by s with the constant byte c.

Starting at the asterisk, it fills the string -- the "hole" we skipped in the memmove call -- with as many '-' as there are characters in 'answer'.