Introduction to CWriting C ProgramsUsing the C Compiler at UMBCInvoking the gcc CompilerThe Result : a.outProgram Development Using gccHello World in CScreenshot of Hello, World ProgramAnatomy of a C ProgramComments in CPreprocessor Directivesint main ( )The Function Bodyprintf (“Hello, World!n”) ;return 0 ;Declaring VariablesDeclaring VariablesMore About VariablesArithmetic Operators in CDivisionDivision (con’t)Getting Input from the UserControl StructuresFunctions in CFunction Example in C1Introduction to CTopicsCompilationUsing the gcc CompilerThe Anatomy of a C ProgramDifferences between JavaScript and C2Writing C ProgramsA programmer uses a text editor to create or modify files containing C code.A file containing source code is called a source file.After a C source file has been created, the programmer must invoke the C compiler before the program can be executed (run).The file must have an extension of .c, i.e filename.c3Using the C Compiler at UMBCInvoking the compiler is system dependent.At UMBC, we have two C compilers available, cc and gcc. For this class, we will use the gcc compiler as it is the compiler available on the Linux system.4Invoking the gcc CompilerAt the prompt, type gcc -ansi -Wall program.c where program.c is the C program source file.-ansi is a compiler option that tells the compiler to adhere to the ANSI C standard.-Wall is an option to turn on all compiler warnings (best for new programmers).5The Result : a.outIf there are no errors in pgm.c, this command produces an executable file, which is one that can be executed (run).The gcc compiler names the executable file a.out .To execute the program, at the prompt, type a.outAlthough we call this process “compiling a program,” what actually happens is more complicated.6Program Development Using gcc Source File pgm.cProgram Object Code File pgm.oExecutable File a.outPreprocessorModified Source Code in RAMCompilerLinkerOther Object Code Files (if any)Editor7Hello World in C/* Filename: hello.c * Author: Brian Kernighan & Dennis Ritchie * Date written: ?/?/1978 * Description: This program prints the greeting * “Hello, World!” */#include <stdio.h>int main(){ printf(“Hello, World!\n”); return 0;}8Screenshot of Hello, World Program9Anatomy of a C Programprogram header commentpreprocessor directives (if any)int main ( ){ statement(s) return 0 ;}10Comments in CAll comments must begin with the characters /* and end with the characters */11Preprocessor DirectivesLines that begin with a # in column 1 are called preprocessor directives (commands).Example: the #include <stdio.h> directive causes the preprocessor to include a copy of the standard input/output header file stdio.h at this point in the code.This header file was included because it contains information about the printf ( ) function that is used in this program.12int main ( )Every program must have a function called main. This is where program execution begins.main() is placed in the source code file as the first function for readability.The reserved word “int” indicates that main() returns an integer value.The parentheses following the reserved word “main” indicate that it is a function.13The Function BodyA left brace (curly bracket) -- { -- begins the body of every function. A corresponding right brace -- } -- ends the function body.The style is to place these braces on separate lines in column 1 and to indent the entire function body 3 to 4 spaces.14printf (“Hello, World!\n”) ;This line is a C statement.It is a call to the function printf ( ) with a single argument (parameter), namely the string “Hello, World!\n”.Even though a string may contain many characters, the string itself should be thought of as a single quantity. Notice that this line ends with a semicolon. All statements in C end with a semicolon.15return 0 ;Because function main() returns an integer value, there must be a statement that indicates what this value is.The statementreturn 0 ;indicates that main() returns a value of zero tothe operating system.A value of 0 indicates that the program successfully terminated execution.16Declaring VariablesWhen declaring a variable in C, you must also specify the type of the variable.Examples of variable declarations: int hw1Grade ; float finalAverage ;17Declaring Variables When we declare a variableSpace is set aside in memory to hold a value of the specified data typeThat space is associated with the variable nameThat space is associated with a unique addressVisualization of the declaration int hw1Grade ; type namehw1Grade garbage18More About VariablesC has three basic predefined data types:Integers (whole numbers)int, long int, short int, unsigned intFloating point (real numbers)float, doubleCharacterschar19Arithmetic Operators in C Name Operator ExampleAddition + num1 + num2Subtraction - initial - spentMultiplication * fathoms * 6Division / sum / countModulus % m % n20DivisionIf both operands of a division expression are integers, you will get an integer answer. The fractional portion is thrown away.Examples : 17 / 5 = 3 4 / 3 = 1 35 / 9 = 321Division (con’t)Division where at least one operand is a floating point number will produce a floating point answer.Examples : 17.0 / 5 = 3.4 4 / 3.2 = 1.25 35.2 / 9.1 = 3.86813What happens? The integer operand is temporarily converted to a floating point, then the division is performed.22Getting Input from the User#include <stdio.h>int main (){ int num1, num2; printf("Please enter the first value: "); scanf("%d", &num1); printf("Please enter the second value: "); scanf("%d", &num2); printf("The first number is: %d.\n", num1); printf("The second number is: %d.\n", num2); return 0 ;}23Control StructuresAll of the control structures we discussed in JavaScript are similar in C: if, if-else-if, while, do-while, for and switch.One difference is that you may only compare integers or characters in a switch statement.24Functions in CWe write functions in C for the same reasons we do in JavaScriptTo be able to re-use code in other programsTo keep us from having to