C pointers and calling methods? - c

Question

I'm new to C and I'm having a hard time understanding how to call methods with pointers. Currently this code should reverse a null-terminated string, but I get the errors
main.c:8:12: error: use of undeclared identifier 'sas'
char* N = sas;
^ main.c:10:10: warning: incompatible integer to pointer conversion passing 'char' to parameter of type
'char *'; remove * [-Wint-conversion]
reverse(*N);
^~ ./header.h:3:27: note: passing argument to parameter 'N' here EXTERN void reverse(char *N);
My actual code is this:
Main:
#include <stdio.h>
#include <stdlib.h>
#include "header.h"
int main(int argc, char *argv[])
{
char* N = sas;
reverse(*N);
}
reverse:
#include <stdio.h>
#include "header.h
#include <stdlib.h>
void reverse(char *str)
{
char* end = str;
char temp;
printf("this is *str: %c\n", *str);
if (str)
{
while (*end)
{
++end:
}
end--;
while (str < end)
{
temp = *str
*str++ = *end;
*end-- = temp;
}
}
}
header.h:
#define EXTERN extern
EXTERN void reverse(char *N)
thanks for the help and time!

Answer 1

int main(int argc, char *argv[])
{
char* N = "sas";
reverse(*N);
}
First you make N point to a string constant. Then you try to reverse what N points to. But since N points to a string constant, you're trying to reverse a string constant. By definition, constants cannot have their values changed.

Answer 2

First of all, there're many syntax errors within that piece of code:
'sas' what is that? your compiler thinks it's a variable but can't find any with that name. if you wanted to put a "sas" string, then:
char* N = "sas";
inconsistant brackets. More closing brackets than opening ones, and no opening bracket after declaring your function.

Answer 3

As I understand it, you are trying to reverse a string. This is just a slight modification of your code.
Full Source:
#include <stdio.h>
#include <stdlib.h>
void reverse(char *N);
int main(int argc, char *argv[])
{
char strSas[] = "sas";
reverse(strSas);
}
void reverse(char *str)
{
char* end = str;
char temp;
if(str) {
printf("this is *str: %c\n", *str);
while(*end) {
++end;
}
end--;
while(str < end) {
temp = *str;
*str = *end;
*end = temp;
++str;
--end;
}
}
}