PHP - Increment a value

[KaksFaits]

I'd like to increment a value in a 3-digits format.For example:\[code\]$start_value = http://stackoverflow.com/questions/3875315/000;while () {do something;$start_value++;}\[/code\]In this way I have this result:\[code\]$start_value = http://stackoverflow.com/questions/3875315/000;$start_value = 1;$start_value = 2;$start_value = 3; \[/code\]and so oninstead of \[code\]'001', '002', '003'\[/code\]How I can accomplish this result?