Programming in C: Basics

1 Programming in C: Programming in C: BasicsBasicsCS10001:CS10001: Programming & Data StructuresProgramming & Data StructuresDept. of CSE, IIT KGPP allab DasguptaPallab DasguptaProfessor, Dept. of Computer Sc. & Engg.,Professor, Dept. of Computer Sc. & Engg.,Indian Institute of Technology KharagpurIndian Institute of Technology KharagpurTypes of variableTypes of variable We must We must declare declare thethetype type of every variable we use in C. of every variable we use in C. Every variable has a Every variable has a typetype( ( intint) and a ) and a This prevents some bugs caused by spelling errors (misspelling This prevents some bugs caused by spelling errors (misspelling variable names).)

2 Variable names).Dept. of CSE, IIT KGP Declarations of types should always be together at the top of main Declarations of types should always be together at the top of main or a function (see later).or a function (see later). Other types are Other types are charchar, , signedsigned, , unsignedunsigned, , longlong, , shortshortand and and KeywordsIdentifiers and Keywords IdentifiersIdentifiers Names given to various program elements (variables, Names given to various program elements (variables, constants, functions, etc.)constants, functions, etc.) May consist of May consist of lettersletters, , digitsdigitsand the and the underscoreunderscore( _ ) character, ( _ ) character, with no space no space of CSE, IIT KGP First character must be a letter or character must be a letter or underscore.

3 An identifier can be arbitrary identifier can be arbitrary long. Some C compilers recognize only the first few characters of the Some C compilers recognize only the first few characters of the name (16 or 31).name (16 or 31). Case sensitiveCase sensitive area , AREA and Area are all different. area , AREA and Area are all and Invalid IdentifiersValid and Invalid Identifiers Valid identifiersValid identifiersXXabcabcsimple_interestsimple _interesta123a123 LISTLIST stud_namestud_name Invalid identifiersInvalid identifiers10abc10abcmymy--namename hello hello simple interestsimple interest(area)(area)%rate%rateDept. of CSE, IIT KGPstud_namestud_nameEmpl_1 Empl_1 Empl_2 Empl_2avg_empl_salaryavg_empl_salary%rat e%rateAnother Example: Another Example: Adding two numbersAdding two numbersREAD A, BREAD A, BSTARTSTART#include < >main(){int a, b, c;scanf( %d%d , Variable DeclarationVariable DeclarationDept.)}

4 Of CSE, IIT KGPC = A + BC = A + BPRINT CPRINT CSTOPSTOP scanf( %d%d , c = a + b;printf( %d ,c);}#include < >#include < >/* FIND THE LARGEST OF THREE NUMBERS *//* FIND THE LARGEST OF THREE NUMBERS */main()main(){{int a, b, c, max;int a, b, c, max;scanf ( %d %d %d , &x, scanf ( %d %d %d , &x, Example: Example: Largest of three numbersLargest of three numbersSTARTSTARTREAD X, Y, ZREAD X, Y, ZISISX > Y?X > Y?YESYESNONODept. of CSE, IIT KGPif (x>y) if (x>y) max = x;max = x;else max = y;else max = y;if (max > z)if (max > z)printf( Largest is %d , max);printf( Largest is %d , max);else printf( Largest is %d , z);else printf( Largest is %d , z);}}ISISMax > Z?)))

5 Max > Z?X > Y?X > Y?Max = XMax = XMax = YMax = YOUTPUT MaxOUTPUT MaxOUTPUT ZOUTPUT ZSTOPSTOPSTOPSTOPYESYESNONOL argest of three numbers: Largest of three numbers: Another wayAnother way#include < >/* FIND THE LARGEST OF THREE NUMBERS */main(){int a, b, c;scanf ( %d %d %d , &a, Dept. of CSE, IIT KGPscanf ( %d %d %d , &a, if ((a>b) && (a>c)) /* Composite condition check */printf ( \n Largest is %d , a);elseif (b>c) /* Simple condition check */printf ( \n Largest is %d , b);elseprintf ( \n Largest is %d , c);}#include < >#define PI * Function to compute the area of a circle */float myfunc (float r){float a;a = PI * r * r;return (a); /* return result */Use of functions: Use of functions: Area of a circleArea of a circleMacro definitionMacro definitionFunction definitionFunction definitionFunction argumentFunction argumentDept.))}

6 Of CSE, IIT KGPreturn (a); /* return result */}main(){ float radius, area;float myfunc (float radius);scanf ( %f , area = myfunc (radius);printf ( \n Area is %f \n , area);}Function argumentFunction argumentFunction declarationFunction declaration(return value defines the type)(return value defines the type)Function callFunction callStructure of a C programStructure of a C program Every C program consists of one or more C program consists of one or more functions. One of the functions must be called One of the functions must be called The program will always begin by executing the main program will always begin by executing the main function.)

7 Each function must contain:Each function must contain: A function A function headingheading, which consists of the function , which consists of the function namename, , followed by an optional list of followed by an optional list of argumentsargumentsenclosed in enclosed in Dept. of CSE, IIT KGPfollowed by an optional list of followed by an optional list of argumentsargumentsenclosed in enclosed in A list of argument A list of argument A A compound statementcompound statement, which comprises the remainder of the , which comprises the remainder of the Programming StyleDesirable Programming Style ClarityClarity The program should be clearly program should be clearly written.

8 It should be easy to follow the program should be easy to follow the program logic. Meaningful variable namesMeaningful variable names Make variable/constant names meaningful to enhance program variable/constant names meaningful to enhance program clarity. area instead of a area instead of a radius instead of r radius instead of r Dept. of CSE, IIT KGP radius instead of r radius instead of r Program documentationProgram documentation Insert comments in the program to make it easy to comments in the program to make it easy to understand. Never use too many use too many comments. Program indentationProgram indentation Use proper proper indentation.

9 Structure of the program should be immediately of the program should be immediately Example: Indentation Example: Good StyleGood Style#include < >/* FIND THE LARGEST OF THREE NUMBERS */main(){int a, b, c;Dept. of CSE, IIT KGPscanf( %d%d%d , &a, if ((a>b) && (a>c))printf( \n Largest is %d , a);elseif (b>c)printf( \n Largest is %d , b);elseprintf( \n Largest is %d , c);}Indentation Example: Indentation Example: Bad StyleBad Style#include < >/* FIND THE LARGEST OF THREE NUMBERS */main(){int a, b, c;scanf( %d%d%d , &a, Dept. of CSE, IIT KGPscanf( %d%d%d , &a, if ((a>b) && (a>c))printf( \n Largest is %d , a);elseif (b>c)printf( \n Largest is %d , b);elseprintf( \n Largest is %d , c).)))}

10 }Data Types in CData Types in Cintint:: integer quantity:: integer quantityTypically occupies 4 bytes (32 bits) in occupies 4 bytes (32 bits) in :: single character:: single characterTypically occupies 1 bye (8 bits) in occupies 1 bye (8 bits) in of CSE, IIT KGPfloatfloat:: floating:: floating--point number (a number with a decimal point)point number (a number with a decimal point)Typically occupies 4 bytes (32 bits) in occupies 4 bytes (32 bits) in :: double:: double--precision floatingprecision floating--point numberpoint Some of the basic data types can be augmented by using certain Some of the basic data types can be augmented by using certain data type qualifiers:data type qualifiers: shortshort longlong signedsigned unsignedunsignedDept.