I copied a small piece of code 
i.e

// Setting PWM properties
const int freq = 30000;
const int pwmChannel = 0;
const int resolution = 8;
int dutyCycle = 200;

from  ESP32 with DC Motor – Control Speed and Direction | Random Nerd Tutorials into ESP32-CAM Remote Controlled Car Robot Web Server | Random Nerd Tutorials 
And I get the error
Compilation error: conflicting declaration ‘const int resolution’
 
Both the codes compiles separately without error!