C – Summary of C functions

As you know, C functions are basic building blocks in every C program. We have given key points those to be kept in mind for using existing C library functions and writing our own functions in a C program efficiently.

Key points to remember while writing functions in C:

• All C programs contain main() function which is mandatory.
• main() function is the function from where every C program is started to execute.
• Name of the function is unique in a C program.
• C Functions can be invoked from anywhere within a C program.
• There can any number of functions be created in a program. There is no limit on this.

• There is no limit in calling C functions in a program.
• All functions are called in sequence manner specified in main() function.
• One function can be called within another function.
• C functions can be called with or without arguments/parameters. These arguments are nothing but inputs to the functions.
• C functions may or may not return values to calling functions. These values are nothing but output of the functions.

• When a function completes its task, program control is returned to the function from where it is called.
• There can be functions within functions.
• Before calling and defining a function, we have to declare function prototype in order to inform the compiler about the function name, function parameters and return value type.

• C function can return only one value to the calling function.
• When return data type of a function is “void”, then, it won’t return any values
• When return data type of a function is other than void such as “int, float, double”, it returns value to the calling function.
• main() program comes to an end when there is no functions or commands to execute.
• There are 2 types of functions in C. They are, 1. Library functions 2. User defined functions