User:LABoyd2/If to manual 151006

If Statement

---

Performs a test to determine if the actions in a sub scope should be performed of not.

If (test) scope1
If (test){scope1}
If (test) scope1  else  scope2
If (test){scope1} else {scope2}

Parameters

test: Usually a boolean expression, but can be any value or variable.

See here for true or false state of values.

See here for boolean and logical operators

Do not confuse the assignment operator '=' with the equal operator '=='

scope1: one or more actions to take when test is true.

scope2: one or more actions to take when test is false.

if (b==a)  cube(4);
if (b<a)  {cube(4); cylinder(6);}
if (b&&a) {cube(4); cylinder(6);}
if (b!=a)  cube(4); else cylinder(3);
if (b)    {cube(4); cylinder(6);} else {cylinder(10,5,5);} 
if (!true){cube(4); cylinder(6);} else  cylinder(10,5,5); 
if (x>y)   cube(1, center=false); else {cube(size = 2, center = true);}
if (a==4) {}                      else  echo("a is not 4");
if ((b<5)&&(a>8))  {cube(4);      else cylinder(3);}
if (b<5&&a>8)       cube(4);      else cylinder(3);

Since 2015.03 variables can now be assigned in any scope. Note that assignments are only valid within the scope in which they are defined - you are still not allowed to leak values to an outer scope. See Scope of variables for more details.

Nested if

The scopes of both the if() portion and the else portion, can in turn contain if() statements. This nesting can be to many depths.

 if (test1) 
 {
   scope1 if (test2) {scope2.1}
          else {scope2.2}
 }
 else
{
  scope2 if (test3) {scope3.1}
         else {scope3.2}
}

When scope1 and scope2 contain only the if() statement, the outer sets of braces can be removed.

 if (test1)
   if (test2) {scope2.1}
   else {scope2.2}
 else
   if (test3) {scope3.1}
   else {scope3.2}

One evolution is this:

else if

      if(test1) {scope1}
 else if(test2) {scope2}
 else if(test3) {scope3}
 else if(test4) {scope4}
 else           {scope5}

Note that else and if are two separate words. When working down the chain of tests, the first true will result use its scope. All further tests will be skipped.

example
  
if((k<8)&&(m>1)) cube(10);
else if(y==6)   {sphere(6);cube(10);}
else if(y==7)    color("blue")sphere(5);
else if(k+m!=8) {cylinder(15,5,0);sphere(8);}
else             color("green"){cylinder(12,5,0);sphere(8);}