Introduction to C Programming

Features of C Programming

  • C is a small language having lesser number of keywords than Java or pascal.
  • C is a native language of Unix, Linux. Not only that many of the windows packages, database programs, graphics libraries are written in C program
  • C is portable – it provides standard set of libraries that work on the same way with all machines
  • C is modular, as it supports functions to divide the program in to sub program
  • C is efficient on most machines, because certain constructs are machine dependant.

Structure of a C program

  • Comments
    • the comments are usually ignored by the compiler
    • so this part informs about the author of the program
    • what is the usefulness of this program
    • updation or creation of the program
    • Example: //  - Single line comment
    • /* ----- multi line comments    ….*/
  • Preprocessor Directives
    • before the compiler runs, the preprocessing takes place.
    • the preprocessors are prefix with a symbol #
    • Examples: #include, #define, #ifdef, #pragma, etc.
  • Function prototypes
    • This is to inform the compiler that the following functions are defined in this program.
    • it specifies the name of the function, arguments or parameters and return type and it ends with a semicolon
    • Ex: int sum(int,int);
  • Global Variables
    • Global variables which are declared above all the functions
    • As the name says, they are available to all the functions of that program
    • They are usually stored in the RAM
  • Main Function
    • main is the function which is main to the entire program
    • Every C program should have a main function
    • syntax: int main() { }
    • Earlier, the main program will return nothing, ie void, but now the compilers are instructing us to provide a return type for the main() function
  • User defined functions
    • After the main() function, the user defined functions are defined, as per the function prototype declared in the program
    • The function can be defined above the main function also, in that case there is not need for function prototype
    • Syntax:

int sum(int a, int b)


int f;


return f;



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