how to solve this error pwm.c(76): error: #137: expression must be a modifiable lvalue
17 #define left1 IOPIN0 = (1 << 11)
18 #define right1 IOPIN0 = (1 << 8) . . . 74 if(center)
75 return 0;
76 else if(left1 | right1 ) {... ..
Are you _sure_ you want your #defines to perform assigns?
You could start by giving some serious thought to whether it is good idea to use actions (like "write this number to this register"), whose value is a constant, as conditions in an if() clause.
The superficial issue is that your macros lack sufficient parentheses.
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