Transfer a variable to earier point without goto - caching

Question

How to write this without goto:
ob_start();
$a = 0;
echo "START of LEFT<br />";
begin:
if($a > 0) {
echo "CONTENT LEFT: $a<BR />";
<VERY DIFFICULT ALGORHITM>
goto end;
}
<... ALL THE REST CODE OF LEFT ...>
echo "END of LEFT<br /><br />";
$output1 = ob_get_contents();
ob_end_clean();
ob_start();
echo "START of CENTER<br />";
$a = 5; goto begin;
end:
<... ALL THE REST CODE OF CENTER ...>
echo "END of CENTER<br />";
$output2 = ob_get_contents();
ob_end_clean();
// print it
echo $output1.$output2;
To get this echo:
START of LEFT
CONTENT LEFT: 5
END of LEFT
START of CENTER
END of CENTER
Requirements:
1. I'm not allowed to change the order(CORE( echo $a ), and PLUGIN( $a=5 )):
ob_start();
$a = 0;
<ANY CODE>
echo $a;
$output1 = ob_get_contents();
ob_end_clean();
ob_start();
<ANY CODE>
$a = rand(0,10);
$output2 = ob_get_contents();
ob_end_clean();
2. Output must be generated via ob_get_contents();
But I'm allowed to write ANY CODE in places.
// Solvings
ob_get_contents(); Helps only if want to replace few lines in output HTML CODE, but can't change a value of variable, to change the ALGORHYTM(depends of var value), which generates the random HTML code.
Also,
As I checked my code, I understand, that my code, even with GOTO labels statement , DOES NOT going to change the $output1 content ?. How to do that? Is the only way is to recache the $output1 from his beggining. Or maybe I'm able to do this in other ways?

Answer 1

You are familiar with the concept of methods/functions? If not ( and it seems that chances are.. ) you should really learn something about those first. It's then a piece of cake to split functionality out of a monolithic block of code to small, maintainable pieces of code.

Answer 2

Structured programming - http://php.net/manual/en/language.oop5.php

Answer 3

If i understood well what you want to do I would use recursive functions instead of goto. for example look at this math expression parser i've witten in C some time ago:
#include <cstdio>
const long MAX = 100010;
char S[MAX], *p=S;
long eval();
long termen();
long factor();
int main() {
FILE *fin=fopen("evaluare.in", "r");
FILE *fout=fopen("evaluare.out", "w");
fgets(S, MAX, fin);
fprintf(fout, "%ld\n", eval());
return 0;
}
long eval() {
long r = termen();
while ( *p=='+' || *p=='-' ) {
switch ( *p ) {
case '+':
++p; // go over "+"
r += termen();
break;
case '-':
++p; // go over "-"
r -= termen();
break;
}
}
return r;
}
long termen() {
long r = factor();
while ( *p=='*' || *p=='/' ) {
switch ( *p ) {
case '*' :
++p;
r *= factor();
break;
case '/':
++p;
r /= factor();
break;
}
}
return r;
}
long factor() {
long r=0;
if ( *p == '(' ) { // subexpression
++p; // go over '('
r = eval();
++p; // go over ')'
} else {
while ( *p>='0' && *p<='9' ) { // number
r = r*10 + *p - '0';
++p;
}
}
return r;
}
The main idea is to split the code in functions and where you have let's say:
goto apocalypse
you'll have:
Apocalypse();
That's the long story said short.