I´m trying to make a simple caltulator using PIC18F46K22 microcontroler and UART. However it works only for adding two numbers, even though the strstr cor comparison and finding the “+” / “-“.

Can someone please spot the problem?

Code:

`#include <xc.h>             //-- for XC8 compiler
#include <stdio.h>          //   for printf
#include <ctype.h>
#include <string.h>
#include <stdlib.h>

#define _XTAL_FREQ 32E6

typedef struct
{
    char data[32];
    char full;
    int  index;
} mailbox;


void main(void)
{ 
    
    while(1)
    {
        if(g_mail.full)
        {
            while(!TX1IF);
            char *ptr;
            int num1, num2;
            char operator;
            
  
            // Determine the operator using strstr
            if (strstr(g_mail.data, "+")) {
                operator = '+';
            } else if (strstr(g_mail.data, "-")) {
                operator = '-';
            }


            int result = 0;

            // Perform the calculation
            if (operator == '+') {
                result = num1 + num2;
            } else if (operator == '-') {
                result = num1 - num2;
            }

            // Prepare the result string
            char resultStr[16];
            sprintf(resultStr, "%d", result); // Convert result to a string

            // Send each character in the result string
            for (int i = 0; i < strlen(resultStr); i++) {
                while (!TXSTAbits.TRMT); // Wait for TX buffer to be ready
                TXREG = resultStr[i]; // Send character
            }

            g_mail.full = 0; // Reset mailbox flag
            memset(g_mail.data, 0, sizeof(g_mail.data)); // Clear the data array
        }
    }
}

Thanks everyone for your help and tips!

I have tried changing syntax and few different approches but nothing works. Chat also cannot find a problem and writes the same answe a little bit differently.