$insert = "insert into new_table (name,f_name,contact,country,city,address,age,age_sc,gender,problem,visit,doc,fee,currency,date,c_date) values('$name','$f_name','$phone_no','$country','$city','$add','$age','$age_sc','$gender','$prob','$doct','$fee','$crncy','$a_date',NOW())";
Never build an SQL query by concatenating strings. Sooner or later, you will do it with user inputs, and this opens door to a vulnerability named "SQL injection", it is dangerous for your database and error prone.
A single quote in a name and your program crash. If a user input a name like "Brian O'Conner" can crash your app, it is an SQL injection vulnerability, and the crash is the least of the problems, a malicious user input and it is promoted to SQL commands with all credentials.
SQL injection - Wikipedia[
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SQL Injection[
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SQL Injection Attacks by Example[
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PHP: SQL Injection - Manual[
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SQL Injection Prevention Cheat Sheet - OWASP[
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