CS31

You LuCS31-1K TA

Hello World!

Variable

• Declare Variables before you use ittype variable_list;e.g. int i, j, k;

• Numeric Ranges (textbook page 9)int: double:

• Check its range before you use this type of variable. Make sure the value you want to store in this variable will not be out of its range.

Out of the RangeYou input 8888888888, but it outputs another different number.

I/O

• cin >>• cout <<

Input one word or string

cin>>s;//can only input one word, e.g., only my first name.

getline(cin, s);//can input the whole string, e.g., my first and last name

cin.ignore(10000, '\n')

Use cin.ignore(10000, '\n') after reading a number if the next input will be of a string (using getline)

Arithmatic

• Division: 5/2=2; 5.0/2=2.5– as long as one of the number is a “double” we

have a “double” division.• Mod: 5%2=1 (remainder)• Casting: – int a = 2.5 a = ? 2– (double)5/2 = ? 2.5– (double) (5/2) = ? 2

Visual Studio 2010

Check the output of compiler to see if there is any warning or error every time.

iostream precision

• Default is 6 digits• If “double a = 1234.56789”; “cout << a” will

only display 1234.57• Here you can use “cout.precision(9)” to set the

output as 9 digits.• See the example below.

iostream precision

Be more careful to use “cout”

header file

• #include <string> //standard built-in libraries• #include “ccc_time.h” //user-defined libraries

if …

• if (condition) statement;condition:• non-zero value means true;• zero value means false;

another example

if…else… if (expression) statement;else statement;

Nested if statement:if(){ if() {…} else {…}}else if(){}else{}

Boolean expression

• Greater than or equal: “>=“• Less than or equal: “<=”• Equal: “==”• Not equal: “!=”• Logic expression:– AND: &&– OR: ||– NOT: !

priority• Arithmetic operator > relational operator

10 > 1+2 ↔ 10 > (1+2)• “<<“ operator > logic operatorcout << “true AND false is ” << (true && false);

priority

highest !

> >= < <=

== !=

&&

lowest ||

while loop

while (expression){

statement;}

do{statement;

}while (expression)

example

for loop

for (initialization; condition; increment) {

statement;}

infinite loop:for(;;){}

“continue”

skip the current round loop, go to the next round loop

for(…){

code 1;code 2;continue;code 3;

}

example

“break”

stop the current loop and get out of the loop.

for (…){

code 1;code 2;break;code 3;

}

code 4

example

“goto”

• goto and “lable” must be in the same function.

lable:goto [lable];

another exampleJump out from a deep nested loopfor(…){

for(…){

while(…){

if(…) goto stop;…

}}

}stop:

cout << “Error in program. \n”;//”break” can only jump out from only one loop

Online reference

• Some websites are really helpful for you to learn C++, like http://www.cplusplus.com/

• More detailed reference: Microsoft MSDN library – http://

msdn.microsoft.com/en-us/vstudio/hh388567– http://msdn.microsoft.com/en-us/library/cscc687

y(v=vs.80).aspx

– http://msdn.microsoft.com/en-us/library/3bstk3k5.aspx

Look up “rand()”

My webpage for CS31 1K

http://www.cs.ucla.edu/~youlu/CS31-1K.html