iosday01c Language data types

1. Comments

Single-line Comment
Annotations act as explanations to the code, and annotations are for programmers, not programs.
/*
Multi-line comments
Xcode shortcut Keys
Select All Cmd+a
Copy Cmd+c
Paste Cmd+v
Set cmd+,
Comment cmd+/
Run Cmd+r
Compiling cmd+b
*/

2. Conversion into the system

3. Data type

　　

? float and double difference: accuracy is not the same.     ? float Effective digits are 6 bit .     ? double Effective digits are 15 bit . Number of significant digits: from the number on the left, not 0 , to the exact number , all numbers.

4. Constants, variables

1> Constants : Amount that cannot be changed during program operation
Integer constant 10,-100
Floating-point constants: 20.3, 3.5
Character-type constants: ' A ', ' f ', ' ', ' 1 '

2> variables : Variables can be modified during the program run, variables are a storage area, the contents of the store can be changed
　　　　Definition of a variable
Type modifier variable name = initial value;
=: assignment operator, which assigns a value of 18 to the age

　　　　　 1int age =; 　　

　　　　Variable name naming rules

1. Can only be composed of letters , numbers , underscores ,$ , cannot start with a number

2. cannot have the same name as the system reserved word

3. Variable name names cannot be duplicated

4. See the meaning of the name (specification)

5. Hump nomenclature ( in the case of multiple words, the first letter is lowercase, starting with the second word, capitalized in the first letter)

5. Operators

1> arithmetic operator (+-*/)

2> calculation remainder operator %

The data type on either side of the find operator must be an integer

3> self-increment (self-subtraction) operation + + (-)

　　　　When a self-increment operator appears separately

// value = value + 1;    // value = value + 1;

When a self-increment operator is used in conjunction with another operator

　　　　　　relult = value++; Equivalent to Relut = value, value = value + 1;

　　　　　　relult = ++value; Equivalent to value = value + 1; Relut = value;

　　　　Summary: operator is preceded, self-increment, in the participating Operation　
The operator is then involved in the operation, doing the self-increment operation

4> compound operator　

1        A + = B; // A = a + B; 2 // A = a -B; 3 // A = a * b; 4 // A = A/b; 5 // A = a% B;

6. Expressions, statements

　　expression : An expression consisting of constants , variables , and operators with return values , without semicolons

　　Statement : statement ends with a semicolon, which is the smallest unit of program execution

7, formatted output input

1> formatted output:printf () 　

1 printf ("%4d\n"//  right-aligned accounted for 4-bit output 23 printf (  "%-4d%d\n"//  left-aligned 4-bit output 45 printf (" %04d\n " // with 0 placeholder output

　　　　Placeholders for different types of variables are summarized:

　　　　　　Integral type: Short%d
int%d
Long%ld

unsigned long%lu
Long Long%lld

Float type: float%f
Double%LF

Character type: Char%c

String:%s

Address:%p

　　　　Escape character

　　　　　　

2> Format Input function scanf () 　　　

in scanf input function do not allow to appear \n keyboard and enter

What do you enter in scanf ?　　　　 scanf is extracting data from the keyboard buffer 　

1     intA =0;2printf"Please enter an integer \ n");3scanf"%d", &a);4GetChar ();//Take a character out of the keyboard buffer5Rewind (stdin);//clears all contents of the keyboard buffer6     Charc =0;7printf"Please enter a character \ n");8scanf"%c", &c);9printf"A =%d, c =%c\n", A, c);

iosday01c Language data types