Question about Loop

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for ($i=0; $i < 4; $i++) {
      echo "$i";
}

In this code of PHP :

How PHP read this code for the first time ?
for the first time the result should be 1 2 3 .
because 0 + 1 = 1.
But the result is 0 1 2 3, why ? How ?
I know that number start from 0 , 1 , 2 , 3 , 4 .......
I actually can not usderstand that how PHP read this code for the first time ?

again for this code ::

for ($i=1; $i < 4; $i++) {
      echo "$i";
}

here $i = 1 , so the result should be 2 3 .
because 1 + 1 = 2.
But the result is 1 2 3, why ? How ?


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for the first time when it read $i=1 ,
it fulfil the condition and so it prints ,
then it is not reading $i < 4 ; $i++ .
is that it ?
and from the second time it reading those and continuing ,
And  it will NOT read $i++, if $i < 4 succeed .

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