Input, output and conditional judgment in C language

Table of Contents

Data types, operators and expressions

1.Data type

Basic data types include

Ranges

2. Constants and variables

constant

variable

Define variables

Classification of variables

Why use variables

3.Input and output

Format output function printf()

Output type when printing

Format input function scanf()

4. Arithmetic operators and arithmetic expressions

Two unary operators and five binary operators

Increment/decrement operators

Comma operator and comma expressions

Find byte operator

sizeof operator

strlen function

5.getchar, getch, putchar functions

6. Relational operators and relational expressions

priority

7. Logical operators and logical expressions

8.if statement

9. Conditional operators

10.switch statement

Data types, operators and expressions

1.Data type

Basic data types include

  • integer type
    • Basic integer type (int)
    • short
    • long
    • long long
    • Character type (char)
    • Boolean type (bool)
  • floating point type
    • Single precision floating point type (float)
    • Double precision floating point type (double)

Value range

Data type Value range Bytes
char – 128~127 1 byte (8 bits)
short -32768~32767 2 bytes (16 bits)
int -2147483648~2147483647 4 bytes (32 bits)
long -2147483648~2147483647 4 bytes (32 bits)
long long -9223372036854775808~9223372036854775807 8 bytes (64 bits)
float 1.175*10^-38~3.402*10^38 4 bytes (32 bits)
double 2.225*10^-308~1.797*10^308 8 bytes (64 bits)

2. Constants and variables

constant

Constants include:

  • literal constant
    • Any type: boolean, integer, float, character, string, etc.
  • const modified constant
    • const modifies ordinary variables, resulting in a constant being defined, but this constant can be modified through a pointer
  • #define modified identifier constant
    • The defined identifier does not occupy memory and is just a temporary symbol. This symbol will no longer exist after precompilation.
    • Use: #define MAXSIZE 100
      • All MAXSIZE in the code will be replaced with 100
  • enum constants
    • enum enumeration type name {constant 1, constant 2, constant 3, …};

Variable

Define variables

int a=10;

Classification of variables

Variables are divided into: global variables and local variables

  1. The life cycle of local variables is: the life cycle begins when entering the scope and ends when it exits the scope.
  2. The life cycle of global variables is: the life cycle of the entire program.

When global variables and local variables exist at the same time, local variables are executed first.

The output result of this code is 15

Why use variables

When inputting, you must first define variables, and when looping, you also need to increment or decrement variables…

The auto-increment of the variable i defined here can output a series of increasing numbers.

3.Input and Output

Format output function printf()

Format:
printf(“Format control string”, output list);

Format control: A string enclosed in double quotes that specifies the output format.

Output table column: A list of data to be output, separated by commas, and can be any legal expression.

Output type when printing

Data type Print type
char %c
short %hd
int

%d (decimal)

%o (octal)

%x (hex)
long %ld
long long %lld
float %f
double %lf

< /table>

%e：

There must be one and only one non-zero digit before the decimal point.

Format input function scanf()

Format:
scanf (“format control”, address table column);

Precision cannot be specified when entering data, but width can be specified

4. Arithmetic operators and arithmetic expressions

Two unary operators and five binary operators

Data type Print type
Unsigned number (decimal) %u
String %s
Print a Percent sign (%) %%
float The type retains two decimal places (a total of five decimal places including the decimal point) %5.2f
Output real numbers in standardized exponential form (standard retains six decimal places) %e
Monocular positive +
Monocular negative –
Multiply *
Except /
Modulo %
Addition +
Subtraction –
  • Operators are executed in order from high to low according to their precedence.
  • If one of the two numbers operated with +, -, *, / is of double type, the result will also be of double type. This is because all real numbers are operated on the double type.

increment/decrement operator

int a=1;

a=a + 1;

printf(“%d”,a);

The statement expressing a=a + 1; here can also be written as:

  • a + =1;
  • a + + ;
  • + + a;

But there is still a difference between a + + and + + a

int a=1;

int b=a + + ;

printf(“%d\
“,a);

printf(“%d\
“,b);

int c= + + a;

printf(“%d\
“,a);

printf(“%d\
“,c);

Comma operator and comma expression

//Output 9 9 8

Mainly to make better use of the space in one line and make the code more compact

Look for byte operator

sizeof operator

The sizeof operator is used to calculate the number of bytes occupied by the data type, which is to calculate the space occupied by the data. The unit is bytes, and it is an operator for finding the number of bytes.

For strings, it ends with /0’, and the sizeof operator will also calculate /0’

//Output 8,9,6

strlen function

Remember to add the header file #include when using it

The strlen() function ends when encountering \0’

//Output 3 9

5.getchar, getch, putchar function

  1. The header files required by getchar() and getch() are different. Generally, getchar() is used.
  2. The getchar() function can only receive one character, and its function return value is the character obtained from the input end.
  3. putchar: The putchar function prints its parameters 
     putchar(a);
\t
//equivalent to printf
printf("%c",a);

6. Relational operators and relational expressions

What is obtained are the true or false values of the relational expression.

Priority

Priority from smallest to largest:

Assignment operation (similar to int a=1) –> relational operation (similar to a!=b) –> arithmetic operation (similar to a + b)

7. Logical operators and logical expressions

True and false values of logical operations

Greater than >
Greater than or equal to >=
Less than <
Less than or equal <=
Not equal !=
Equal ==

td>

a b !a !b a & amp; & amp;b a||b
True True False False True True
True False False True False True
False True True False False True
False False True True False False

8.if statement

usage:

if (expression 1){

Statement 1;

}

else if (expression 2){

Statement 2;

}

else{

Statement 3;

}

9.Conditional operator

The conditional operator (?:) is the only ternary operator, which can effectively reduce the amount of code

10.switch statement

usage:

switch(expression){
case constant 1: statement 1
case constant 2: statement 2
default: statement n
break;
}

If a constant value that is not included in the switch statement is entered, the statement after default will be executed.