Introducing C

Week 1 Lecture 2 SE1SA5 1

Introducing C

SE1SA5

Sue Walmsley


Outline

Why C?Standard C librariesA ProgramCommentsCompiling and RunningVariablesInput/OutputData type qualifiers


Why C?

C is a classic language which forms the foundation of many other programming languages

C is widely available, under many operating systemsAs you study C (and then C++) you will learn the theory

of programming and this will help you appreciate other languages You will study C++ later this year

Those following degree courses in the School of Systems Engineering (SSE) will go on to use both C and C++, and many of you will also utilise other languages


Standard C libraries

ANSI C defines a number of standard libraries

The libraries have “header files” which normally have the extension “.h”

For example, most C programs use:stdio.h

Contains input and output functions, types and macro definitions.


Other libraries include:

ctype.hstring.hmath.hstdlib.htime.hlimits.hfloat.h

Look these upand find out what they contain

Hint: before writing something complicated check if there is a library function that does it


A Program

#include <stdio.h>

/* this program produces three lines of output */int main ( ){

printf("This module is called: \n");printf("\t Programming \n");printf("This program is written in: ");printf("C\n");return 0; /* returns successfully */

}


Notes on the program

Save it as name.cC always need a main( ) function

This one returns an int 0Lines starting # are instructions to the preprocessorNames of library files must be in angular brackets < and

>The braces { and } contain statements to be executed In C semicolons ( ; ) are used to terminate statementsC is free format – line breaks and white space can go

between itemsC is case sensitive Int is different to int


Comments and coding standards

In C comments are delimited by /* and */

Use comments to make your program more easily understood by other people and yourself

Commercial firms often have standards for coding and these will include how to comment

Reproduced from the PowerPoints for C How to Program, 4/e by Deitel and Deitel 2004. Reproduced by permission of Pearson Education, Inc. (selected and adapted by SMW)

• Phases of C Programs:

1. Edit

2. Preprocess

3. Compile

4. Link

5. Load

6. Execute

Program is created inthe editor and storedon disk.

Preprocessor programprocesses the code.

Loader puts program in memory.

CPU takes eachinstruction and executes it, possibly storing new data values as the program executes.

Compiler creates object code and storesit on disk.

Linker links the objectcode with the libraries

Loader

Primary Memory

Compiler

Editor

Preprocessor

Linker

Primary Memory

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Disk

Disk

Disk

CPU

Disk

Disk

Compiling and Running


Variables

A variable is like a container in a C program in which a data value can be stored in the computer memory

Variable names:Consist of letters, numbers and underscores ( _ )CANNOT start with a numberCANNOT be C keywords

For example:Num1, num1, _answer


Example of variable use

int num1, num2;int sum;num1 = 2;num2 = 5;sum = num1 + num2;

num1 num2 sum


Basic typesData type Description Examplechar A single byte, holds one

character'A'

int An integer whole number

12

float A floating point number using 32 bits

12.34

double More accurate, using 64 bits

9.123456789

Look up bits and bytes


Data types and printing them

#include <stdio.h>/* illustrates printf */int main ( ){

int num =12;char letter;float fNum;letter = 'A';fNum = 12.34;printf ("num is %d \n", num);printf ("letter is %c \n", letter);printf ("fNum is %f \n", fNum);return 0;

}


Output

num is 12letter is AfNum is 12.340000


Using scanf to read values into variables

int num =12;char letter;float fNum;printf ("please enter a character: ");scanf ("%c", &letter);printf ("please enter a float: ");scanf ("%f", &fNum);printf ("num is %d \n", num);printf ("letter is %c \n", letter);printf ("fNum is %f \n", fNum);return 0;

Note with scanf you must use the ampersand (&) with basic data types (such as int).In this case & is the “addressof” operator and tells the program to store the data in the variable name that follows.


Output

please enter a character: Aplease enter a float: 12.34num is 12letter is AfNum is 12.340000


Formatting Output (int)

int num =12;printf ("num using %%d is %d \n", num);printf ("num using %%1d is %1d \n", num);printf ("num using %%2d is %2d \n", num);printf ("num using %%3d is %3d \n", num);printf ("num using %%4d is %4d \n", num);printf ("num using %%05d is %05d \n", num);printf ("num using %%06d is %06d \n", num);printf ("-num using %%4d is %4d \n", -num);


Output

num using %d is 12num using %1d is 12num using %2d is 12num using %3d is 12num using %4d is 12num using %05d is 00012num using %06d is 000012-num using %4d is -12


Formatting Output (floats)

float fNum = 12.3456;printf ("fNum using %%8.0f is %8.0f end\n", fNum);printf ("fNum using %%-8.0f is %-8.0f end\n", fNum);printf ("fNum using %%8.2f is %8.2f end\n", fNum);printf ("fNum using %%-8.4f is %-8.4f end\n", fNum);


Output

fNum using %8.0f is 12 endfNum using %-8.0f is 12 endfNum using %8.2f is 12.35 endfNum using %-8.4f is 12.3456 end

Note the rounding in the third line.


Data type qualifiers

#include <stdio.h>#include <limits.h>int main ( ){

short int small; long int tall;printf ("Max int:\t %d\n", INT_MAX);printf ("Max long int:\t %d\n", LONG_MAX);printf ("Max shortint:\t %d\n", SHRT_MAX);

printf ("Min int:\t %d\n", INT_MIN); printf ("Min long int:\t %d\n", LONG_MIN); printf ("Min short int:\t %d\n", SHRT_MIN);return 0;

}


Output

Max int: 2147483647Max long int: 2147483647Max shortint: 32767Min int: -2147483648Min long int: -2147483648Min short int: -32768


sizeof operator

printf ("sizeof small %d\n", sizeof (small));printf ("sizeof tall %d\n", sizeof (tall));printf("sizeof short int %d\n", sizeof (short int));printf("sizeof float %d\n", sizeof (float));printf("sizeof double %d\n", sizeof (double)); --sizeof small 2sizeof tall 4sizeof short int 2sizeof float 4sizeof double 8


Summary

Standard C librariesPrograms and commentsCompiling and RunningVariables Input/OutputData type qualifiersNext week –will include

External, static, register variables Casting Arrays Constants and enumeration Preprocessor directives

Introducing C

Documents

Transcript of Introducing C