"C Language" 07-Basic statements and operations

first, the basic statement

The basic language of C is almost the same as in Java, so here's just a simple way to mention

• Loop statements (Do while, while, for)
• Conditional statements (if, if-else, switch)
• Goto statement

 II. Basic Operations

The basic ability of a computer is computing, so the computational power of a language is very important. The reason why C is omnipotent is that it has strong computational power. There are 34 types of operators in C, most of which are identical to those used in Java. Here is a brief introduction.

1. Arithmetic Operators

• + addition operator

• -subtraction operator, or negative operator

• * Multiplication operator

• /Division Operator

• % modulo operator, or call-to-rest operator, requires that both sides are integral

2. Relational operators

• < less operator

• <= less than equals operator

• > Greater than operator

• >= greater than equals operator

• = = equals operator

• ! = does not equal operator

* The result of the relational operation is "true" (for example, 5>=4), which is "false" (such as 5<4).

* In Java, the result of the relational operation is "true" returns True, "false" returns False, with a Boolean type of variable to receive

Boolean B1 = 5 > 4; Trueboolean B2 = 5 < 4; False

There is no Boolean type in the C language

* In the C language, the result of the relational operation is "true" returns 1, "false" returns 0

int a1 = 5 > 4; 1int A2 = 5 < 4; 0

* Also note that in C, any value other than 0 is true, and only 0 is false

So the following is the right approach:

int a = 10;if (a) {    printf ("conditional");} else {    printf ("condition not valid");}

Because A is not 0, it is "true" and the output is:

In Java, the compiler directly complains because the If bracket () can only put a Boolean value.

And so on, the following wording is also true:

int a = 10;if (A = 0) {    printf ("conditional");} else {    printf ("condition not valid");}

The above code is completely reasonable, the compiler will not error, just a warning. Because A is 0, the result is "false" and the output is:

In this sense, C language seems to be much more convenient than Java, in fact there are a lot of traps here:

Suppose you want to judge whether a is 0, then Ben should write if (a = = 0), if you mistakenly write if (a = 0), it would be a very scary thing, because the compiler does not error, such a bug is difficult to find. Therefore, the expression like a==0, preferably written 0==a, if you mistakenly write 0=a, the compiler will directly error.

Not recommended if (A = = 0) {}//recommended if (0 = = a) {}

* In C, you can not save the results of relational operations

Therefore, the following wording is legal:

1 int a = 10;2 a > 10;3 a = = 0;

If it is in Java, the 2nd, 3 line compiler will directly error, but the C compiler appears to be legal, just a warning.

So, here is another trap, assuming that your intention is to assign a value of 0, then Ben should write a = 0; , if you mistakenly write a = = 0; , it will be a very hard to find bug, because the compiler won't make any errors at all. In 1993, the bug almost blew up a $20 million hardware business because if the bug didn't work, the product wouldn't work.

3. Logical Operators

• && Logic and operators

• || Logical OR operator

• ! Logical non-operator

The result of the logical operation is also only two: the establishment is "true", return 1; "false", return 0

4. Assignment Operators

1. Simple assignment operator =: int a = 5;

2. Compound assignment operator

• + = Plus assignment operator. such as a + = 3+1, equivalent to a = A + (3+1)

• -= minus assignment operator. such as a-= 3+1, equivalent to A = A-(3+1)

• *= multiply the assignment operator. such as a *= 3+1, equivalent to a = A * (3+1)

• /= In addition to the assignment operator. such as a/= 3+1, equivalent to A = A/(3+1)

• %= the value of the remainder assignment operator. such as a%= 3+1, equivalent to a = a% (3+1)

5. Self-increment and decrement operators

• + + auto-increment operator. such as A++,++a, are equivalent to a = a+1

• --the self-decrement operator. such as a--,--a, are equivalent to a = A-1

6. Comma operators and comma expressions* The comma operator is primarily used for connection expressions, such as:

1 int a = 9;2 int b = 10;3 4 A = a+1, B = 3*4;

* An expression concatenated with the comma operator is called a comma expression, and its general form is:

Expression 1, expression 2, ..., expression n

The operation of the comma expression is: From left to right, evaluates expression 1, evaluates expression 2, ..., and evaluates expression n

* The value of the entire comma-expression is the value of the last expression

1 int a = 2;2 int b = 0;3 int c;4 5 c = (++a, a *= 2, B = A * 5); 6 7 printf ("C =%d", c);

The result of ++a is 3,a *= 2 results for 6,b = A * 5 result is 30. As a result, the output is:

It is important to note that the right expression is wrapped in parentheses (), if not enclosed in parentheses, that is:

c = ++a, a *= 2, b = A * 5;printf ("c =%d", c);

The output will be: because C = ++a is also part of the comma expression and is independent of the subsequent a *= 2 and B = A * 5

7. Conditional operators and conditional expressions

is actually a three-mesh operator, the general form is: expression 1? Expression 2: Expression 3

int a = (b > 5)? 10:9;

8.sizeof

* sizeof can be used to calculate the number of bytes of memory for a variable or a constant, a data type.

int size = sizeof;p rintf ("10 Bytes:%d", size);

Output: 10 is data of type int, in 64bit compiler environment, int type needs to occupy 4 bytes

* sizeof has 3 different forms

• sizeof (variable \ constant)

sizeof (+); char c = ' a '; sizeof (c);

• sizeof variable \ constant

sizeof 10;char C = ' a '; sizeof C;

• sizeof (data type)

sizeof (float);

Note that it is not possible to write sizeof float;

"C Language" 07-Basic statements and operations