iOS basic operations

<span id="Label3"></p><p>//<br>Main.m//file Name<br>Day2-class//project Name<br>//<br>Created by open on 16/1/5.//date created and created by<br><br>//<br>Single-line Comment: can annotate a piece of code, play the role of explanation, note is the embodiment of our Programmer's programming thinking, Note does not participate in the program Run.<br><br><br>/*<br>This is a multi-line comment.<br>Comd+z: Undo<br>Comd+,: Set<br>Comd+a: Select All<br>Comd+shift+n: Create a new project<br>Comd+[: Let our lines of code move left<br>Comd+]: Let our lines of code move right<br><br>*/<br><br><br>#import: Import<br>#import <>: represents the framework in which our systems are imported (that is, the foundation Framework)<br>#import "": represents the import of files we create ourselves<br><br>#import <Foundation/Foundation.h><br><br><br>Function: it is by function type function name (parameter---> formal parameter, argument)<br>{function body; }<br>VOID stands for none, no return value is required<br>Function: it encapsulates a piece of code snippet<br>void Test ()<br>{<br><br><br>}<br><br><br>Main Function: He is the entrance to our program, The program starts execution, it encounters a return end, the code snippet is written in return 0;<br>int main (int argc, const char * Argv[]) {<br><br><br>@autoreleasepool: It's The syntax of our oc, called the Auto-release Pool.<br>@autoreleasepool {<br>Insert code here ...<br>NSLog (@ ""); This is also the print function in our OC<br>NSLog (@ "Hello, world!");<br>//    }<br><br>Data type:<br>Format: type modifier variable name = value;<br>Semicolon (;): A concluding sentence representing our code snippet<br>int NMU = 7;<br>Float type only outputs 6 decimal places by default<br><br>FLOAT score = 88888.923456;<br>printf ("%f\n", score);<br>%f output only 6 decimal places by default<br>printf ("%.7f\n", score);//represents a seven decimal place after the output decimal point<br>%f after printing, float precision is 6 digits after the decimal point, but the valid number is 7 bits<br>? Then we want to print out 3.1415926 what to do<br>The number of valid digits for a double is 15 bits<br>Double D1 = 3.1415926;<br>printf ("%.7lf\n", d1);<br><br>If you want to output 7 bits then we can use double<br>/*<br><br>Float Type: The significant number of digits is 6 bits<br>Double type: the number of significant digits is 15 bits<br> <br>*/<br>Character Type:<br>Character type format: type modifier variable name = ' ' (single quote);<br>Spaces also represent a character<br>char sex = ' m ';<br>Constant: The amount of time that cannot be changed while the program is running<br>Variable: is the amount of time that can be changed while our program is running<br>A variable is equivalent to a piece of storage space in our memory = number is an assignment operator<br>Variable naming rules:<br>1. can only be composed of numbers, letters, underscores, $, cannot start with a number;<br>2. cannot have the same name as the system reserved word;<br>3. Duplicate variable names cannot be used;<br>4. See the meaning of the name;<br>5. The Hump method is named;<br>#pragma mark--operator---quick Index<br>#pragma mark (hint Word) is a quick index<br><br><br>The first (must be mastered) (hand-copied 10)<br>int NUM1 = 21;<br>int num2 = 25;<br>Then we define a Third-party variable to store the value we exchange.<br>int temp = 0;<br>Give the value of NMU1 to Temp<br>temp = num1;<br>Give the value of num2 to NUM1<br>NUM1 = num2;<br>Give the value of temp to num2<br>num2 = temp;<br>printf ("num1 =%d", num1);<br>printf ("num2 =%d", num2);<br><br><br>The second type:<br>You do not need to use additional variables to swap with ADD and subtract<br>Define two variables of type int<br>/* int num3 = 34;<br>int num4 = 43;<br>num3= num3 + num4;<br>num4= num3-num4;//(num3 + num4)-num4<br>num3= num3-num4;//(num3 + num4)-num4<br>printf ("num3 =%d\n", num3);<br>printf ("num4 =%d\n", num4);<br><br>Third Kind<br>Use XOR or (^);<br>int a =3,b = 4;//the same data type can be placed in the same rowset named<br>A = a^b;<br>b = a^b;<br>A = a^b;<br>printf ("a =%d\n", a);<br>printf ("b =%d\n", b);<br><br><br>*/<br><br>//+,-,*,/<br>A variable of type int is defined as an initial value of 5;<br>int a = 5;<br>A variable b that defines an int type has an initial value of 10;<br>int B = 10;<br>Define a Third-party variable to receive our A and B's and<br>int result = 0;<br>result = A + b;<br>printf ("result =%d\n", result);<br><br>-; subtraction;<br>int c = 10;<br>int d = 5;<br>int JF = 0;<br>JF = c-d;<br>printf ("JF =%d\n", jf);<br><br>Multiplication (division)<br><br>self-increment, self-reduction<br>+ + in front, the first to +1, and then participate in the operation,<br>+ + in the after, the first operation and then to self +1<br>//<br>int a = 2;<br>int B = 4;<br>int c = 0;<br>c = a+++b++;//c = (a++) + (b++);<br>printf ("%d\n", c);<br><br>Char: occupies one byte, range -128~127<br><br>Char type constant storage, which corresponds to the corresponding ASCII code table value corresponding to the storage<br>char a = ' a ';<br>printf ("%d\n", a);//our Corresponding character can be occupied with%d, but we will print the value of our corresponding ASCII code TABLE.<br>//<br><br>#pragma mark--composite operator--<br>// += -= *= /=<br>int a = 4;<br>int c = 0;<br>c + = a; c = c+a;<br>c = 0+4;<br>printf ("%d\n", c);<br>int B = 6;<br>int d = 7;<br>int e = 0;<br>e-=b;//<br>printf ("%d\n", e);<br>//    //*=<br>E *= d;//e = e*d<br>printf ("%d\n", e);<br><br>#pragma mark---printf---<br><br>printf ()//formatted output function<br>scanf () Format input function (blocking Function)<br><br>/*<br>***********<br>hello***<br>***********<br>*/<br>printf ("***********\n***hello***\n***********\n");<br>To define a variable of type int and assign an initial value of 18 to it, and print<br>int age = 18;<br>printf ("age=%d\n", age);<br>printf ("*\n * *\n* * *\n");<br>Scanf: Blocking function;<br>int age1 = 0;//is assigned a value of 0, in order to clear the data<br>printf ("please Enter an age: \ n");<br>Scanf: executes when a newline (carriage Return) is encountered<br>1. Receive the value of a single variable, if we enter a carriage return or tab will be ignored before entering<br>//<br>scanf ("%d", &age1);//& It is a fetch address character, the function is: the data entered by our user is stored in our corresponding variable<br>printf ("age1=%d\n", age1);<br><br>Please enter two numbers and sum<br>int NUM1 = 0;<br>int num2 = 0;<br>int sum = 0;<br>printf ("please enter two numbers: \ n");<br>scanf ("%d%d", &num1,&num2);//note: The address (&) when the "%d%d" do not add anything (for example, \ n), Otherwise the output is not correct, plus (\ N) For example (%d\n%d\n) will be offset (\ n); (,) For example (%d,%d) must be entered (,) otherwise only the value of NUM1 is Output.<br>scanf ("%d", &num1);<br>scanf ("%d", &num2);<br>sum = num1+num2;<br>printf ("sum =%d\n", sum);<br>/*<br>scanf use Note:<br>1. In our scanf input function do not add \ n, because \ n will offset the carriage return, if you want to continue to make the program execution, then in the console input a string of English (random input), will continue to offset<br>2. We scanf function in the user input, according to "", some internal symbols to enter (that is, what to enter What)<br>3. The best thing to do is to add nothing (the direct placeholder is Ok)<br><br>*/<br>#pragma mark--memory buffers--<br>int a =2, B = 3;<br>char C = ' 0 ';<br>printf ("please Enter the corresponding data type: \ n");<br>scanf ("%d%c%d", &a,&c,&b);<br>printf ("a=%d\nc=%c\nb=%d", a,c,b);<br><br>Format Control for Output:<br>/*<br>%2d:2 indicates the width of the output, less than two bits, the first fill the space, and the output is aligned<br>%02d:0 representative, less than 2, when the first 0<br>%-4d:-represents that the content of the output is left justified<br>*/<br><br><br>int age = 9;<br>printf ("%d\n", age);<br>printf ("%2d\n", age);<br>printf ("%02d\n", age);<br>printf ("%-4d\n", age);<br><br><br> <br><br><br><br><br><br>Encounter return 0; End<br>Return 0;<br><br><br>}<br><br></p><p><p>iOS basic operations</p></p></span>