Functions in C

Function:

• Function is block of instructions that performs a task.
• C Program execution starts with main() function.
• OS invokes main() function automatically to start the program.

The prototype(syntax) of main() function as follows:

• The prototype of main as follows
  • int main(int argc, char* argv[])
• The signature of function is used to read arguments from command line.
• main() signature is optional if we are not using command line arguments.

Any one of following definitions allowed for main():

• We can define main() method in any one of the following ways.
• Main() method by default return type is int, hence we return any int value to avoid compilation warnings.

Library functions:

• C library is a collection of header files.
• Header file is a collection of functions.
• In the previous examples, we used few functions.

We can write user functions depend on application:

• Function is a block of instructions that performs a task.
• Function takes input, process input and return output.
• The Syntax and Definition of function as follows

Every function consists:

1. Prototype: It is a single statement; it is used to specify the function memory representation.
2. Definition: It is a block. It contains function logic to perform the task.
3. Call: It is a single statement. It is used to access the function logic

Calling the function:

• We must call the function explicitly after definition.
• Function logic executes only when we invoke.
• Main() function executes implicitly by OS.
• Other functions must be called explicitly by programmer.