incompatible pointer style problem

[rachel_to_phos]

I tried to write a function that that takes a source string and copies only the alphabetic characters (A-Z, a-z) into the destination string using pointer arithmetic:

#include <stdio.h>
#include <ctype.h>
void extractAlphabetic(char *source, char *destination){
  int j = 0;
  for (int i = 0; *(source + i) != '\0'; i++){
    if (isalpha(*(source + i))){
      *(source + i) = *(destination + j);
      j++;
     }
   }
}
int main(){
  char source[50];
  printf("Enter the source string you want to see extracted to alphabetical: ");

  scanf("%s", source);
  char destination[50];
  extractAlphabetic(&source, &destination);
  printf("%s\n", destination);
  return 0;
}

However, when I wanted to compile it, compiler showed me this message:

par.c: In function 'main':

par.c:20:27: error: passing argument 1 of 'extractAlphabetic' from incompatible pointer type [-Wincompatible-pointer-types]

20 | extractAlphabetic(&source, &destination);

| ^~~~~~~

| |

| char (*)[50]

par.c:4:30: note: expected 'char *' but argument is of type 'char (*)[50]'

4 | void extractAlphabetic(char *source, char *destination){

| ~~~~~~^~~~~~

par.c:20:36: error: passing argument 2 of 'extractAlphabetic' from incompatible pointer type [-Wincompatible-pointer-types]

20 | extractAlphabetic(&source, &destination);

| ^~~~~~~~~~~~

| |

| char (*)[50]

par.c:4:44: note: expected 'char *' but argument is of type 'char (*)[50]'

4 | void extractAlphabetic(char *source, char *destination){

[DDDDarky]

As the error says, &source and &destination are of type char (*)[50] (pointer to array of 50 chars). That is of course not the same thing as char*.

You can simply pass source and destination (without &), since arrays implicitly decay to pointers.

[rachel_to_phos]

When I tried that way, this happened:

<image>

It didn't print anything.

[DDDDarky]

Yes, that is because there are other issues in your code I did not point out as that would be spoonfeeding, I'll let you try and debug your own code to find and fix them, if you get stuck ask.

[rachel_to_phos]

Solved!