Android JNI Programming (ii) Basic data type of--c language, output function, input function

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Before we learn the C data types, let's review the basic data types and their features in Java: Basic data type 1. There are eight basic data types in Java and one reference data (String) type as follows:

byte      1字节  char      2字节  short 2字节 int 4字节 float 4字节 long 8字节 double 8字节 boolean 

2. What are the types of C? We can take a look.

int        4字节char       1字节float 4字节double 8字节long 4字节short 2字节signed 4字节unsigned 4字节void 1字节

The 3.C language provides us with a function that can be used to calculate the length of a type directly, so it is very convenient to know the length of a type.

Length of calculation type: sizeof (type) returns a length of type int main () {The length of the calculation typeprintf"Byte of type int:%d\n",sizeofint));printf"Char type occupies bytes:%d\n",sizeofchar));printf"The byte of type float:%d\n",sizeoffloat));printf"The byte of the double type:%d\n",sizeof (double)); printf ( "Long" of bytes:%d\n ",  sizeof (long)); printf ( "short type of bytes:%d\n",  sizeof (short)); printf ( "signed type of bytes:%d\n",  sizeof (signed)); printf ( "unsigned type takes up bytes:%d\n", sizeof (unsigned)); printf ( "void type occupies bytes:%d\n",  sizeof (void))}            

4. Careful you may find out why a Boolean type is missing? How do you judge that? The original C language used the non-0 and the "%" is true and false.

    //C语言中boolean类型，0表示为false，非零表示true    if(0) { printf("false\n"); } else { printf("true\n"); }

Some differences between the 5.Java basic data types and C languages:

1. The length of the char type in Java is 2 bytes, and the length in the C language is 1 bytes
2. The length of a long type in Java is 8 bytes, and the length in C is 4 bytes (C99 (99) Standard provisions: Long type, not less than shaping)
3. No byte in C language
4. Boolean type in c language, 0 = false, nonzero means true
5. Singed: Signed Range: 128 ~ 127–> ( -2^7 ~ 2^7-1)
6. Unsinged: Unsigned range: 0 ~ 255–> (0 ~ 2^8-1)
7. void: No type, representing any type
8. There are no string types in the C language, but you can use a char array to represent

Two: Output function 1. The output function is much simpler. than Java's System.out.println()And a few more code.

printf("内容");//如果需要换行我们只需要添加换行符就行了printf("\n","内容");

2. Write a simple output statement

main() {    char c = ‘a‘;    printf("c==\n",c);    //使docs窗口停留 system("pause");}

Why didn't we export our A? The original C language in the output to use the placeholder, then we add a placeholder to try

main() {    ‘a‘;    printf("c==%c\n",c);    //使docs窗口停留 system("pause");}

Now it's time to get the output, so let's talk about the placeholder for this ghost thing.

• int–>%d
• Long int–>%ld
• Char–>%c
• Float–>%f
• Short Plastic –>%HD
• Double–>%lf
• Hex Output –>% #x
• unsigned (unsigned) –>%u
• String –>%s
• Octal –>%o

Different types have to be exported with different placeholders, otherwise the accuracy is lost.

3. Now let's define some variables and output them

Main () {char c =' A ';int i =12345678; Long L =526247678; float F =3.1415; Double d =3.1415926535;//Back analysis, why do you write char* str="I am a string"; printf ("c==%c\n", c); printf ("i==%d\n", i); printf ("l==%ld\n", L); printf ("f==%f\n", f); printf ("d==%lf\n", D); printf ("str==%s\n", str); //Make Docs window stay system ("pause");}            

Gee ~, the output of f behind how much more than two a 0? In the C language, the default is to retain six decimal places, in order to retain the corresponding number of digits, you need to add ". Reserved digits" In the following code:

printf("f==%.4f\n",f);//效果就是f==3.1415，图就不贴了

Three: Input function 1. Introduction to input functions

scanf("占位符",内存地址);

2. Write a simple input function, type a number from the console and print it to the console

int i;printf("亲！请输入一个数字：\n");//&i,就是取i的地址，也就是把从控制台接收到的数据赋值给i。scanf("%d",&i);printf("输入的数字为：%d\n",i);

3. Use arrays to represent our strings, use a For loop to print the group contents

    //定义一个数组[]必需在数组名右边     char arr[]= {‘H‘,‘e‘,‘l‘,‘l‘,‘o‘}; //for循环需要将变量在外面，不能像java一样定义在里面 int j; for(j=0; j<5; j++) { printf("arr[%d]=%c\n",j,arr[j]); } //C语言中没有String类型，但是可以用char数组来表示 //直接将数组输出 printf("arr：%s\n",arr);

4. We can also enter a string from the console

    printf("请输World：\n");    //声明数组和数组长度    char arr2[5]; //将控制台的内容赋值给arr2 scanf("%s",&arr2); printf("arr2：%s\n",arr2);

5. In the output of the array you will find that you will output a lot of messy things, because: the array is a contiguous memory space, you need to add an array at the back of the' + 'Indicates the end

    char arr3[]= {‘a‘,‘b‘,‘c‘,‘d‘,‘e‘,‘\0‘}; printf("arr3==%s\n",arr3);

This article is about here, the next will continue to learn the C language pointers and other content, the pace of learning can not stop, continue to move forward.

Android JNI Programming (ii) Basic data type of--c language, output function, input function