Computer Programming and Problem Solving

Ke shuwei

1. What is the meaning of problem solve?

2. How to solve it?

3. What is computer programming?

4. What is basic knowledge for solving?

Computer Problem

1. the problem about computer itself

Blue Screen of Death (BSoD)

Computer Problem

2. Utilize computer to solve the real world problem.The real world problem is called Computer Problem.

This is the meaning of Computer problem in our class we have to solve.

Computer Problem

Problem: find the largest number between three number(12, 15, 18)

Human:a primary student knows it is 18.

Computer: zzzZZZZZ~~~~~~ NO IDEA

Computer Problem

The computer can not solve the problem which a primary student can solve.why we need it?

Computer problemIf we assume the computer can solve this problem.i.e,it can check a number is prime or composite.

Problem: find all the prime number between 1 and 10000?

Human: yes,i can. But i think it will take 5 hours or more.

Computer: too easy,only 10 secs i need.

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

..... }

How to utilize computer to solve problem

• I know C language ,i can write down C code to solve it.

• This is the only way to solve it?

Nope,I know Java. I can write down Java code to solve it.

C++, Ruby .....

What is the computer programming?

Utilize any language code to solve the problem in computer.

C or Java or ...?

1. Same Target:solve the problem.

2. There are thousands of Languages,which one shoud pick?

How to become a good programmer?

• Do i need to know every language?– Too much knowledge.– How can i learn all of them?– i only can live 100 years. ^-^

• What can we do?

What can we do?

• Language is nothing more than a tool to solve the problem.

Learn basic knowledge for all languages

Basic knowledgeProblem: find the largest number between three

numbers(12, 15, 18)

12 < 15, 15 < 18, 12 < 18

Using basci knowledge in different language to solve problem.

C

Java

Connection

• Syntax is different

• if .. else if... else.. is same.

• Operator is same ( >, (),{})

• Declaration is same(int a,...)

• Algorithm(rules) is same – use folwchart to describe algorithm

One more problem

• find all the prime number between 1 and 100.

C

Java

Connection

• if control statements• for conrol statements• operator ( %, = , <= ..)

• Syntax is different• Algorithm(logic) is different

What we have to learn for all programming lanuage?

1.Algorithm (the method to slove problem) if you want to find all prime number,first, you

should know what is prime number.Then,using different algorithm to solve it.

What we have to learn for all programming lanuage?

2. Basic operator is almost same in all language

(>, >=, !=, &&, & .. 1 > 2 ? 1 : 2)

3.Control statements if ... eles if ..else for ... while ... do ... While.. all nested control statements

Why?

If we have learned one language,we can easy to learn other languages.Because

the logic of (method) solving problem is same.

So far, we have taken more than one month to finish three assignments using C language.But I belive that all of you just spent one day to learn syntax of java,then you can finish those assignments less than one day easily.

How?

Be patient to learn basic knowledge,do not care about that i do not know java,ruby..

In our class,we using c.

Let us C

C_code_Convention

• Code conventions are important to programmers for a number of reasons:– 80% of the lifetime cost of a piece of software

goes to maintenance.– Hardly any software is maintained for its whole life

by the original author.– Code conventions improve the readability of the

software, allowing engineers to understand new code more quickly and thoroughly.

An example

Code convention

Basic convention

1.write down comments

2.one statement one line

3.indent every substatement

4.choose variable name close to its meaning ( a or isPrime?)

If..else..

if (condition){

CS1;CS2;...

}/* end of if */

Next statement;

if (condition) CS;

Next statement;

if (condition) CS;

Next statement;

Braces

If ....else...

if (condition){

CS1;CS2;...

}else{

ES1;ES2;...

} /* end of if */

Next statement;

Nested if.. else ..if (a > b){

if ( a > c)a largest; elsec largest;

}else{

if ( b > c)b largest;

elsec laregest;

} /* end of if */

Next statement;

Nested if.. else ..int a = 5, b = 10, c = 9;if (a > b)

if ( a > c)a largest; elsec largest;

else if ( b > c)

b largest;else

d laregest;Next statement;

int a = 5, b = 10, c = 9;if (a > b)

if ( a > c)a largest; elsec largest;

else if ( b > c)b largest;

elsed laregest;

Next statement;

OUTPUT: d largest

int a = 5, b = 8, c = 9, d = 10; if ( a > b) printf("1"); else if ( a > c) printf("2"); else if ( a > d) printf("3"); else printf("4");

int a = 5, b = 8, c = 9, d = 10; if ( a > b) printf("1"); else if ( a > c) printf("2"); else if ( a > d) printf("3"); else printf("4");

OUTPUT: 4

Nested

if (a > b)if ( a > c)

a largest; elsec largest;

elseif ( b > c)

b largest;else

c laregest;

Next statement;

Every else corresponds if which is cloest to it

Nestedint a = 5, b = 4, c = 6;if (a > b)

if ( a > c)printf(“1”);

elseprintf(“2”);

Next statement;

OUTPUT: 2

int a = 5, b = 4, c = 6;if (a > b){

if ( a > c)printf(“1”);

}elseprintf(“2”);

Next statement;

OUTPUT:

Tips

In C,true is any nonzero value and false is zero.

if (1) printf("1");if (2) printf("2");If (!2) printf("3"); if (0) printf("4");If (!0) printf ("5");

Output:125

isPrime

Relational and logical operators

•Operator Meaning

< less than<= less than or equal to> grater than>= grater than or equal to== equal to!= not equal to|| or&& and

Relational Operator Meaning

== equal to

Assignment Operator Meaning

= assign value

• a == b means: a equal to b then return ture else return false

• a = b means: assign the value of b to a

• if ( a == b) correct • if ( a = b) incorrect

compound condition

int a = 5, b = 8, c = 9, d = 10; if ( a > b) printf("1"); else if ( a > c) printf("2"); else if ( a > d) printf("3"); else printf("4");

compound conditionint a = 5, b = 8, c = 9, d = 10;

if ( a < b && a < c && a > 10) printf(“1”);

elseprintf(“2”);

if( true && true && false) = false

if( true && true && true) = ture

if( true || false|| false) = true

if( false|| false || false) = false

compound condition

if ( 1 && 2 && 3) printf("1");

else printf("2");

if ( 1 && !2 && 3) printf("1");

else printf("2");

if ( 0 || 2 && 3 && 4) printf("1");

else printf("2");

if ( 0 || 2 && 3 && 0) printf("1");

else printf("2");

Precedence of c operatorOperator category Operators Precedence

Parentheses,brace ( ), [ ] 1

Unary operator -,++, --, !, `, & 2

Multiplicative operators *, /, % 3

Additive operator +, - 4

Shift operators <<, >> 5

Relation operators <, <=, >, >= 6

Equality operator ==, != 7

Bitwise operator &, ^, | 8

Logical operators &&,|| 9

Conditional operators ?, : 10

Assignment operators =,+=,-=,*=, /=,%= &=, ^=, |=, <<=,>>=

11

Comma operator , 12

if ( 10 - 9 -1 ) printf("1"); else printf("2");

Output: 2

if ( 10 – (9 -1) ) printf("1"); else printf("2");

Output: 1

Conditional Operator

<relation expression> ? <value1> : <value2>

if ( relation expression) return value1;

else return value2;

if ( relation expression)statement1;

else statement2;

<relation expression> ? <statement1>:<statement2>

ExampleC = 5 < 4 ? 5 : 4;

3 1 2 2 precedence operator

Return value

5 > 4 ? printf("1") : printf("2");

statemment

max = a > b ? ( a > c ? a : c) : ( b > c ? b :c);

Thank you!

http://wwww.cpps2010.info

shuwei.ke@gmail.com

Assignment1.Find the largest number in four numbers.Draw flawchart.(10,2,3,20)

2.Find the largest number in four numbers.(using conditional operator)

3.Enter the month,printout the season 11,12,1 -- winter 2, 3, 4 --- spring 5, 6, 7 --- summer 8, 9, 10 -- autumn

4.Enter the marks,printout grade.

90 - 100 A 80 – 90 B 70 – 80 C 60 – 70 D below 60 fail