C language learning log 12.5

One . Two dimensional array

Format ：int a[x][y]: The representative definition has x That's ok y Columns of the matrix , It can also be y That's ok x Columns of the matrix , In order to conform to Linear Algebra , Generally, we think it is the first case .

Two . Array application ：

 eg： When an array is used as an argument in a function , Often you have to use another parameter to pass in the size of the array

3、 ... and .Sizeof:

An operator , Single purpose . In fact, it gets the storage space occupied by data in memory , Count in bytes

(1). For data types ： Format ：sizeof(type);

(2) For variables ： Format ：sizeof(name);

eg:sizeof Operators cannot be used with functions ！！！

(3) As a result, ： The integer is usually 4 Bytes , Single precision is also 4 individual , Double precision floating point numbers are 8 individual , The character type is generally 1 individual

Four . The pointer

& Is used to get the address of the variable , His operands must be variables . Is the address the same size as int About depends on compiler

int i; printf("%p",&i);

* Is a unary operator , The value of the variable used to access the address represented by the pointer variable , It can be an R-value or an l-value .

int k=*p;     *p=k+1

Tips: An array in a function is a pointer, that is ：

int *a And int a[] Equivalent

Array variables are special pointers , Its own expression address so

int a[10]; int*p=a // No need & Address fetch

But the elements of an array represent variables , Need to use & Address fetch

a == &a[0]

[] Operators can be used for arrays or pointers

p[0] <==> a[0]

* Operator can do , You can also do

 *a =25;

The array variable is const The pointer to , So it can't be assigned

int a[] <==> int *const a=..