Performing XOR byte comparisons with chars

Question

I'm trying to perform an XOR byte operation on every 3rd byte in an unsigned char array in my program. I'm having a type conversion error occur when I attempt to compile the program.

my declarations

unsigned char *s;
FILE *fp;
char ch;
int count = 0;
unsigned char *load = malloc(sizeof(char));
int i = 0;

s = "s";

and this is where the error is occurring...

for (i = 3; i < count;)
{
    temp = (load[i-1] ^ s);
    temp2 = (load[i] ^ s);
            i = i + 3;
}       

once I can get the XOR operation to work, I'll be setting load[i-1] = temp, right now I'm just trying to get the operation to compile and hopefully work.

Thanks in advance for any help / insight.

EDIT* Updated to give temp data type and show how unsigned char *load = malloc(sizeof(char)) is being used to take from data from a file.

char temp, temp2;


while ((ch = fgetc(fp)) != EOF)
{
    load[i++] = ch;
}

and here is the error it is producing...

main.c:14:4: warning: assigning to 'unsigned char *' from 'char [2]' converts between pointers to integer types with different sign [-Wpointer-sign]

    s = "s";
      ^ ~~~

main.c:86:21: error: invalid operands to binary expression ('int' and 'unsigned char *')

            temp = (load[i-1] ^ s);
                    ~~~~~~~~~ ^ ~

main.c:87:20: error: invalid operands to binary expression ('int' and 'unsigned char *')

            temp2 = (load[i] ^ s);

Answer 1

You are allocating memory to hold only one unsigned char in

unsigned char *load = malloc(sizeof(char));

Then you are trying access the third character using load[i-1].

Update

The compiler error is very clear about the nature of the error

main.c:86:21: error: invalid operands to binary expression ('int' and 'unsigned char *')

        temp = (load[i-1] ^ s);

Perhaps you meant to use:

        temp = (load[i-1] ^ s[0]);

About the other compiler message, you can take care of that by initializing s when it is defined.

unsigned char *s = "S";

instead of assigning to it later.