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ECE 246(INTRODUCTION TO C

PROGRAMMING)CHAPTER 2:

INPUT AND OUTPUT

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Learning Outcomes Able to apply the programming development

procedure

Able to understand the usage of printf withdifferent data types of variables

Able to understand the usage of scanf with

different data types of variables

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Lesson Outline

Programming development procedure

printf

scanf

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Programming development procedure1. Analyze the problem

2. Develop a solution

3. Code the solution

4. Test and correct the program

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Procedure 1: Analyze the problem Basic analysis: determine and understand the

input items and the desired outputs items to be

produced.If necessary, do:

Extended analysis: obtain additional info

about the problem so that you can thoroughlyunderstand what is being asked and how to

achieve the result

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Procedure 2: Develop a solution Design & development: algorithm for

transforming the input items into the desired

outputs Top-down approach: start with the most

general solution and refine it into clearly

defined tasks

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Procedure 3: Code the solution Code the solution algorithm in C

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Procedure 4:

Test & Debug the Program Select test data

If error(s) found, make correction

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ExampleThe electrical resistance, rof a metal wire, in

ohms is given by the formula: r = (ml)/awhere mis the resistivity of the metal; lis thelength of the wire (feet); and ais the cross-sectional area of the wire (circular mills).Using this info, write a C program to calculate

the resistance of a wire that is 125 feet long,cross sectional area of 500 circular mills, andis copper. Resistivity of copper, mis 10.4.

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Step 1 Key problem statement: to calculate the

resistance of the wire

Output: resistance Inputs: m, l and a

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Step 2

Given formula: r = (ml)/a

Pseudocodes:

Assign values to m, l and a

Calculate the resistance using the formula

Display the result

Do manual calculation to verify

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Step 3

#include

Int main()

{

float resistivity, area, length, resistance;

resistivity = 10.4;

area = 500;

length = 125;

resistance = (resistivity * length)/ area;

printf(The resistance of the wire (in ohms) is %f \n, resistance);

return 0;

}

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Step 4

Verify the correctness of the program

Try with different set of data and check with

manual calculation

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Exercise

Write a C program to calculate the total

resistance of a series circuit. In such a circuit,

the total resistance is the sum of all 56 ohm,33 ohm and 15 ohm resistors.

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printf

C function for output

Used for printing/displaying text

For string:printf ("..some string...");

For integer:

printf ("Integer = %d", integer name); For float

printf ("Integer = %f", float name);

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scanf

C function for input

Gets input from the keyboard

Examples of scanf usage:

int i;

char ch;

float x;

scanf ("%d %c %f", &i, &ch, &x);

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1 /* Fig. 2.5: fig02_05.c2 Addition program */3 #include4

5 /* function main begins program execution */6 intmain( void)7 {8 intinteger1; /* first number to be input by user */9 intinteger2; /* second number to be input by user */10 intsum; /* variable in which sum will be stored */11

12 printf( Enter first integer\n ); /* prompt */13 scanf( %d , &integer1 ); /* read an integer */14

15 printf( Enter second integer\n ); /* prompt */16 scanf( %d , &integer2 ); /* read an integer */17

18 sum = integer1 + integer2; /* assign total to sum */19

20 printf( Sum is %d\n , sum ); /* print sum */21

22 return0; /* indicate that program ended successfully */2324 } /* end function main */Enter first integer45Enter second integer72Sum is 117

Definitions of variables

scanfobtains a value from the

user and assigns it to integer1

scanfobtains a value from theuser and assigns it to integer2

Assigns a value to sum

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More Symbols

& - is called ampersand (address operator in C)

followed by a variable name. When combined a

variable name, it tells scanf the location in memory

at which the variable is located. The value for the

variable is then stored in the location

% - is called conversion specifier, tells scanf or

printf what types of data it is going to read. Printfand scanf treat this symbol as a special character that

begins conversion specifier

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Memory Concepts

Variable names correspond to locations in the

computer's memory

Every variable has a name, a type, a size and avalue

Whenever a new value is placed into a variable

(through scanf, for example), it replaces (and

destroys) the previous value

Reading variables from memory does not change

them

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Memory location showing thename and value of a variable.

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Memory locations after bothvariables are input.

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Memory locations after acalculation.

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Standard algebraicequality operator orrelational operator

C equality orrelationaloperator

Example ofC condition

Meaning of C condition

Equality operators

== x == y xis equal to y

!= x != y xis not equal to y

Relational operators

> x > y xis greater than y

< x < y xis less than y

>= x >= y xis greater than or equal to y

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Exercises:

Fill in the blanks

True/False

Correct the error

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References

Burgess, M. (1999), C Programming Tutorial

(K&R version 4)

Deitel, P.J. & Deitel, H.M. (2007), C How To

Program, Pearson International Edition

http://www.space.unibe.ch/comp_doc/c_manu

al/C/CONCEPT/data_types.html

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