Functions

• function declaration: typeName functionName(typeName1 argName1, ...);
  double performSum(double op1, double op2);
• function call: varName = functionName(argName1, ...) ;
  double d = performSum(1.0, 2.1);
• return control to calling code: return value ;
  

  double performSum(double op1, double op2) {
  return op1 + op2;
  }