Need help completing a code using the test cases and restrictions given:

#$1$ The user is prompted to enter a pseudo arithmetic command. The input must be verified to be grammatically correct.

$2.$ The string and character type library cannot be used under

any circumstances. You are encouraged to develop your own

functions to perform any similar operations that are needed. This includes $($ strlen$(),$ strcpy$(),$ strcmp$(),$ islower$())$

$3.$ No changes to the code in main. Your code must be placed in functions. Additional functions are encouraged