C language knowledge Summary (1), C language knowledge Summary

C language knowledge Summary (1), C language knowledge Summary

Data Types in C Language

Variable Storage

 

Variable instance

int b = 10;int a = 20;

Scanf Functions

int age;scanf("%d",&age);

Note: % d reads a decimal integer % o reads an octal integer % x or % X reads a hexadecimal integer

When multiple data is input using the scanf function, what is the delimiter in the middle of each value? What is input? If each value is separated by a space, each time we enter an integer, we must enter a delimiter, which can be a space, a tab, or a carriage return.

Do not include \ n in the first parameter of scanf, for example, scanf ("% d \ n", & a); this will cause the scanf function to fail.

Arithmetic Operation

The remainder after the division of two integers % both sides can only be positive and negative integers, depending on the value on the left of %

Forced type conversion

double a = (double)(1 / 2);

Sizeof

Function: used to calculate the memory bytes occupied by a variable, a constant, or data type.

Usage: sizeof (variable \ constant) sizeof variable \ constant sizeof (data type)

Condition judgment

In C, "any non-0 value is true, and only 0 is false"

Notes for Link comparison:

• =,! In Relational operators ,! = Has the same priority. <, <=,>,> = has the same priority, and the former has a lower priority than the latter: 2 = 3> 1

• The Union direction of Relational operators is "from left to right": 4> 3> 2

• The priority of Relational operators is less than that of arithmetic operators: 3 + 4> 8-2

Logical operation

1. & logic and

1> use format Condition A & Condition B

2> the calculation result is 1, that is, "true", and 0, that is, "false", only when Condition A and Condition B are both true"

3> the operation process always determines whether Condition A is true.

• If Condition A is true, then judge whether Condition B is true. If Condition B is true, the result of Condition A & Condition B is 1, that is, true ", if Condition B is not true, the result is 0, that is, "false"

• If Condition A is not true, Condition B will not be judged whether it is true. Because Condition A is no longer true, regardless of Condition B, the result of "Condition A & Condition B" must be 0, that is, "false"

4> note

• If you want to determine whether the value of a is within the range of (3, 5), do not write it as 3 <a <5, because the Union direction of Relational operators is "from left to right ". For example, if a is 2, it calculates 3 <a, that is, 3 <2. The condition is not true and the result is 0. Compare with 5, that is, 0 <5. The condition is true and the result is 1. Therefore, the result of 3 <a <5 is 1 and the condition is true. That is to say, when the value of a is 2, the value of a is within the range of (3, 5. This is obviously incorrect. The correct judgment method is: (a> 3) & (a <5)

• C language: any non-0 value is true, and only 0 is false ". Therefore, logic and values are also applicable to numerical values. For example, the result of 5 & 4 is 1, which is "true"; the result of-6 & 0 is 0, which is "false"

2. | logical or

1> use format Condition A | Condition B

2> when Condition A or condition B is set to 1 (both Condition A and Condition B are true), the result is true "; if neither Condition A nor Condition B is true, the result is 0, which is false ".

3> the operation process always determines whether Condition A is true.

• If Condition A is true, Condition B will not be judged whether it is true. Because Condition A is true, regardless of Condition B, the result of "Condition A | Condition B" must be 1, that is, "true"
• If Condition A is not true, then judge whether Condition B is true. If Condition B is true, the result of Condition A | Condition B is 1, that is, true ", if Condition B is not true, the result is 0, that is, "false"

3 ,! Non-logical

1> use format! Condition

2> the calculation result is false or false.

4. Priority

• The priority of logical operators is: parentheses ()> minus sign->!> Arithmetic Operators> Relational operators >&>||

• Expression! (3> 5) | (2 <4) & (6 <1): Calculate first! (3> 5), (2 <4), (6 <1), the result is 1, and the formula becomes 1 | 1 & 0, and then 1 & 0, formula 1 | 0. The final result is 1.

• Expression 3 + 2 <5 | 6> 3 is equivalent to (3 + 2) <5) | (6> 3). The result is 1.

• Expression 4> 3 &&! -5> 2 is equivalent to (4> 3 )&&((! (-5)> 2), the result is 0.

Three-object Operator

For conditional expression B? X: y. Calculate Condition B and then judge. If the value of B is true, the value of x is calculated and the calculation result is the value of x. Otherwise, the value of y is calculated and the calculation result is the value of y.