‘C’ Programming Structures and Commands

‘C’ Programming Structures and Commands By Sidhant Garg

Brief Introduction Of C • C was developed between 1969-1973 by Dennis Ritchie at Bell Laboratories for use with the Unix Operating System. • Unlike previously developed languages C provides facilities for structured programming and allows lexical variable scope and recursion • C is one of the most popular programming languages and there are a very few computer architecture for which the C compiler does not exist.

Structure of C C programs basically contains the following: • Preprocessor Commands • Variables • Constants • Input/output • Functions

Preprocessor commands • The #include pre-processor directive is used to link required library files to the main program file (.cpp) • Some of the common header files and their functions are as follows: • Stdio.h : Standard input /output functions • Math.h: Basic math functions such as tan, log, pow(x,y) etc. • String.h: String operations such as strcpy, strcat etc. • Stlib.h: Standard functions such as malloc, rand, srand etc. • Ctype.h: Character classification functions such as isalnum, isalpha, isdigit etc. • Iso646.h: To use macros for logical operators • E.g. #include<stdio.h> void main() { int x; scanf(“%d”,x); //needs the stdio.h header file }

Example of a program to convert celsius to fahrenheit • #include <stdio.h> • /* print Fahrenheit-Celsius table • for fahr = 0, 20, ..., 300 */ • main() • { • intfahr, celsius; • int lower, upper, step; • lower = 0; /* lower limit of temperature scale */ • upper = 300; /* upper limit */ • step = 20; /* step size */ • fahr = lower; • while (fahr <= upper) { • celsius = 5 * (fahr-32) / 9; • printf("%d\t%d\n", fahr, celsius); • fahr = fahr + step; • }

Variables – Data types • In C, variables can be broadly of the following data types: • char – character type • char stringname [x] (x=1,2..n)- string of ‘x’ characters • int array [x] – array containing ‘x’ elements • int- integer type • float- real numbers including decimals etc. • double- extended form of float (larger range) • The above can also be used in conjunction with the following ‘datatype’ modifiers: • long • short • signed • unsigned cont…

Variables – Data types cont... • In addition to the previously described standard datatypes, C allows the following user defined datatypes: • typedef- Allows users to change the name of a standard data type. For e.g. typedef float money will allow the user to use money as a data type • enum- Enumerated data types similar to C++ e.g. enum color{red,blue,white} • struct- • Structures are heterogeneous user-defined datatypes • They are often used to create nodes and lists • They are like the data members of classes but do not have the concept of associated functions ` e.g. struct features{ int height; double weight; char[5] color; }

Constants • In C, constants can be defined in the following two ways- • Using #define e.g. #define pi 3.14 • Using const e.g. const double x=3.0 • Constants are often declared globally instead of being used directly in the main program.

Input / Output • User input from the keyboard is done using ‘scanf ‘ • Output to the screen is done using ‘printf’ • Here are the format specifiers that are required • %d - int • %c - char • %f - float • %lf -double • %s -string • %x- hexadecimal • For e.g. #include<stdio.h> void main() { int x; scanf(“Enter integer: %d”,x); printf(“The integer you entered is: %d,x,”. Goodbye!”); }

Functions • Functions are modules or subprograms that accept certain parameters and return values to the calling function / main program • They have the following format: Return_type function_name(parameters) { local variables; C statements; return return_value; }

In C all the function arguments are passed by value. This means that the functions are given the values of it arguments in temporary variable rather than the originals. • It usually leads to more compact programs with fewer extraneous variables, because parameters can be treated as conveniently initialized local variables in the called routine

For example, here is a • version of power that makes use of this property. • /* power: raise base to n-th power; n >= 0; version 2 */ • int power(int base, int n) • { • int p; • for (p = 1; n > 0; --n) • p = p * base; • return p; • } • The parameter n is used as a temporary variable, and is counted down (a for loop that runs backwards) until it becomes zero; • there is no longer a need for the variable i. Whatever is done to n inside power has no effect on the argument that power was • originally called with.

Other Concepts • Operators and Expressions • Arrays • Linked Lists • Pointers • Stacks and Queues • Hash Tables

QUESTIONS

‘C’ Programming Structures and Commands