original file

this is unedited

process

• variables are evaluated by fetching values from memory
• constants sometimes fetch from memory, other times they're part of the machine language instruction
• if an operand is a parenthesized expression: evaluate all operands and operators first

side effects

• functional side effects: when a function changes either one of its parameters or a global variable

int a = 5;  
  
int fun1() {  
     a = 17;  
     return 3;  
}   
  
void main() {  
     a = a + fun1();  
}

how to solve?

1. disallow functional side effects

• no two-way parameters in functions
• no nonlocal references in functions
  • DISADVANTAGES:
    • in C all subprograms can only return one value., To return more than one value you would need to place the values in a struct and return the struct.
    • Global variables are necessary when efficiency is important and there is a need to avoid parameter passing. An example would be the symbol table used by compilers.

2. Write the language definition to state the order of evaluating operands and demand that implementors guarantee that order

• DISADVANTAGES: Limits some compiler optimizations that involve reordering operand evaluations.
• Java's language definition guarantees that operands are evaluated left to right.