PHP calculator solution

The PHP calculator php makes a calculator. Why does the page refresh as long as it is computed? but the value of the first text box remains unchanged, and the value of the second text box is gone, is this the default situation .. Below is my code? Why ?? & Lt ;! DOCTYPE & nbsp; html & nbsp; PUBLIC & nbsp; PHP calculator
Why does a calculator made by php only require a little calculation? the page is refreshed, but the value of the first text box remains unchanged, and the value of the second text box is gone. Is this the default case .. Below is my code? Why ??








$ Mess = "";

If (isset ($ _ POST ["sub"]) {

If ($ _ POST ["num1"] = ""){
$ Mess. = "The first number cannot be blank!
";
} Else {
If (! Is_numeric ($ _ POST ["num1"]) {
$ Mess. = "The first number must be a number!
";
}

}
If (is_numeric ($ _ POST ["num1"]) {
If ($ _ POST ["num2"] = ""){
$ Mess. = "The second number cannot be blank!
";
} Else {
If (! Is_numeric ($ _ POST ["num2"]) {
$ Mess. = "The second number must be a number!
";
} Else {
If ($ _ POST ["opt"] = "/" & $ _ POST ["num2"] = 0 ){
$ Mess. = "The divisor cannot be 0 ";
}

}
}
}


}

?>




Calculator


If (isset ($ _ POST ["sub"]) {
Echo' ';
If (! $ Mess ){
$ Sum = 0;
Switch ($ _ POST ["opt"]) {
Case "+ ";
$ Sum = $ _ POST ["num1"] + $ _ POST ["num2"]; break;
Case "-";
$ Sum = $ _ POST ["num1"]-$ _ POST ["num2"]; break;
Case "*";
$ Sum = $ _ POST ["num1"] * $ _ POST ["num2"]; break;
Case "/";
$ Sum = $ _ POST ["num1"]/$ _ POST ["num2"]; break;
Case "% ";
$ Sum = $ _ POST ["num1"] % $ _ POST ["num2"]; break;
}

Echo "result: {$ _ POST ['num1']} {$ _ POST ['opt']} {$ _ POST ['num2'] }={ $ sum }";

} Else {
Echo $ mess;
}

Echo'';
}


?>









?

No score. thank you !!!! Input