operatorprecedence.pde

来自「This is processing for java examples.」· PDE 代码 · 共 59 行

/**
 * Operator Precedence
 * 
 * If you don't explicitly state the order in which
 * an expression is evaluated, they are evaluated based
 * on the operator precedence. For example, in the statement
 * "4+2*8", the 2 will first be multiplied by 8 and then the result will
 * be added to 4. This is because the "*" has a higher precedence
 * than the "+". To avoid ambiguity in reading the program, 
 * it is recommended that is statement is written as "4+(2*8)".
 * The order of evaluation can be controlled through placement of
 * parenthesis in the code. A table of operator precedence follows below.
 * 
 */
 
// The highest precedence is at the top of the list and 
// the lowest is at the bottom.
// Multiplicative: * / %
// Additive: + -
// Relational: < > <= >=
// Equality: == !=
// Logical AND: &&
// Logical OR: ||
// Assignment: = += -= *= /= %=

size(200, 200);
background(51);
noFill();
stroke(51);

stroke(204);
for(int i=0; i< width-20; i+= 4) {
  // The 30 is added to 70 and then evaluated
  // if it is greater than the current value of "i"
  // For clarity, write as "if(i > (30 + 70)) {"
  if(i > 30 + 70) {
    line(i, 0, i, 50);
  }
}

stroke(255);
// The 2 is multiplied by the 8 and the result is added to the 5
// For clarity, write as "rect(5 + (2 * 8), 0, 90, 20);"
rect(4 + 2 * 8, 52, 90, 48);
rect((4 + 2) * 8, 100, 90, 49);
  
stroke(153);
for(int i=0; i< width; i+= 2) {
  // The relational statements are evaluated 
  // first, and then the logical AND statements and 
  // finally the logical OR. For clarity, write as:
  // "if(((i > 10) && (i < 50)) || ((i > 80) && (i < 160))) {"
  if(i > 20 && i < 50 || i > 100 && i < width-20) {
    line(i, 151, i, height-1);
  } 
}