C programs are built from functions, variables, expressions, and statements. File input and output allow a program to read data from files and save processed results. In this exercise, students practice file handling in C by reading text one character at a time and checking the result carefully. c programs are built from functions, variables, expressions, and statements. file input and output allow a program to read data from files and save processed results. in this exercise, students practice file handling in c by reading text one character at a time and checking the result carefully.