Without using built-in functions or third party library

[Student555]

How would one determine if a string literal is a digit, alphabetic character or symbol character (!,@, {, }, $, ^, %, etc) without relaying on ready made functions? Explanation with some sample code would be nice.

[SakurasouBusters]

Simple.
1. Use simple logic with if statements.
if (c >= 'a' && c <= 'z')

2. Use a table.
const char *numTable = "0123456789";

[cire]

Is there a reason you're specifying a string literal as opposed to a string?