# Php > Algorithms Code Examples

## This algorithem checks if an Israeli ID (9 digits) number is valid

``` This algorithem checks if an Israeli ID (9 digits) number is valid The algorithem (MOD 10) is based on Error Brett code from example 74. The algorithem might work on various ID's cause MOD 10 is the basis of many ID checksums. Add a comment to this example if this algorithem works for you too. <? // takes a string and returns an array of characters function toCharArray(\$input){ \$len = strlen(\$input); for (\$j=0;\$j<\$len;\$j++){ \$char[\$j] = substr(\$input, \$j, 1); } return (\$char); } function validateID(\$ID){ //Clean spaces \$ID = ereg_replace('[-[:space:]]', '',\$ID); //Grab the test digit \$Bikoret=substr(\$ID,8,1); //Take only 8 left digits of the Id. \$ID = substr(\$ID,0,strlen(\$ID)-1); \$dig = toCharArray(\$ID); \$numdig = sizeof(\$dig); \$j = 0; for(\$i=(\$numdig-1) ; \$i>=0 ; \$i-=2){ \$dbl[\$j] = \$dig[\$i] * 2; \$j++; } \$dblsz = sizeof(\$dbl); \$validate = 0; //Sum all the 2x for(\$i=0 ; \$i<\$dblsz ; \$i++){ \$add = toCharArray(\$dbl[\$i]); for(\$j=0 ; \$j<sizeof(\$add) ; \$j++){ \$validate += \$add[\$j]; } \$add = ''; } //Sum all the 1x for (\$i=(\$numdig-2); \$i>=0; \$i-=2){ \$validate += \$dig[\$i]; } If(\$validate % 10 != 0) { \$Bikoret1=(substr(\$validate, 0, 1) + 1) * 10; } Else { \$Bikoret1=\$validate; } If(\$Bikoret1 - \$validate == \$Bikoret) return 1; else return 0; } ?> ```