C Language Study Notes (5)-sequential Programming

 

1 Statement Overview

 

1.1 normal expression statement: adding a semicolon after an expression is an expression statement. Different from an expression, a statement has no value while an expression has a value.

 

1.2 process control statement: A process control statement is mainly used to control the execution trend of a program and implement various structure methods of the program. It has specific keywords and can be divided into two types: branch and loop.

 

Branch flow control statements: if and switch.

 

Loop flow control statements: for, while, And do while.

 

1.3 jump statement: the jump statement is mainly used to redirect the program from normal execution to other parts. Common jump statements are as follows:

 

Interrupted statements: break and continue.

 

Turning statement: goto.

 

Return Statement: return.

 

1.4 compound statement: it consists of some statements and is placed in braces to form a whole. The sentence pattern is as follows:

 

{

 

Statement 1;

 

Statement 2;

 

......

 

Statement n;

 

}

 

The C language syntax specifies that compound statements are processed as a statement.

 

Sample Code:

 

 

# Include "stdio. h"

Main (){

Int a = 11, B = 21, c = 31;

Printf ("a = % d \ tb = % d \ tc = % d \ n", a, B, c );

{Int B = 22;/* compound statement start */

Float c = 3.3;

Printf ("a = % d \ tb = % d \ tc = % f \ n", a, B, c );

A = B;

}/* Compound statement ends */

Printf ("a = % d \ tb = % d \ tc = % d \ n", a, B, c );

}

The output result is as follows:

 

A = 11 B = 21 c = 31

 

A = 11 B = 22 c = 3.300000.

 

A = 22 B = 21 c = 31

 

The above code can be compared with the following code:

 

 

# Include "stdio. h"

Main (){

Int a = 11, B = 21, c = 31;

Printf ("a = % d \ tb = % d \ tc = % d \ n", a, B, c );

{Int a = 1;

Int B = 22;/* compound statement start */

Float c = 3.3;

Printf ("a = % d \ tb = % d \ tc = % f \ n", a, B, c );

A = B;

}/* Compound statement ends */

Printf ("a = % d \ tb = % d \ tc = % d \ n", a, B, c );

}

Program running result:

 

A = 11 B = 21 c = 31

 

A = 1 B = 22 c = 3.300000

 

A = 11 B = 21 c = 31

 

As you can see, the variables declared in the composite statement only play a role in the composite statement.

 

1.5 null statement: a null statement generally refers to a placeholder with only one semicolon. It is generally used in the initial stage of program design to indicate the function or code to be compiled.

 

1.6 introduction to various statements:

 

 

# Include "stdio. h"

Main (){

Int a = 10, B = 20, c;/* statement */

If (B> a)/* control statement */

{;/* Compound statement */

C = a + B;/* expression statement */

Printf ("% d", c);/* function call statement */

}

Else

;/* Empty statement */

}

2. Relationship between library function calls and input/output

 

2.1 Standard library functions are stored in the function library. Therefore, you must inform the computer of the library to which the function library belongs. This process is a function declaration. For example:

 

# Include "math. h"/* standard mathematical function declaration */

 

Main (){

 

...

 

Y = sin (x);/* call the library function */

 

...

 

}

 

Include is a specific word in the C language. It indicates a file containing. h, which is called a header file.

 

2.2 some input and output standard library functions are provided in C language, such as printf and scanf. the header file stdio. h of the function library must be included in the program.

 

3. format the output.

 

3.1printf: It outputs data to the terminal.

 

Function Format: printf ("format control statement", output item 1, output item 2 ,......);

 

For example: printf ("% f", j); Output floating point type variable j, % f is the control operator.

 

Common Format controllers:

 

% D -- decimal integer, % o --- octal unsigned integer, % f output real number, % s -- string, % c -- output single character, etc.

 

4-character output

 

The putchar function can be used to output 4.1 characters, which has been defined in stdio. h.

 

Sample Code:

 

 

# Include "stdio. h"

Main (){

Char a, B, c;

A = 'C ';

B = 'a ';

C = 'T ';

Putchar ();

Putchar (B );

Putchar (c );

Putchar ('\ n ');

Putchar ('\ 101 ');

Putchar ('B ');

Putchar ('C ');

}

Note: This function cannot output two or more character data.

 

5. format the input.

 

5.1scanf: This function is used to obtain data from the keyboard, format the data, and assign the value to the variable.

 

Call method: scanf (format control statement, input item );

 

6 Character Input

 

6.1 getch () and getche () functions: read a single character.

 

The difference between the two is that the getch () function does not display the characters read back to the screen, but getche () is displayed.

 

Sample Code:

 

 

# Include <stdio. h>

Main ()

{

Char c, ch;

C = getch ();/* read a character from the keyboard and do not return it to the character variable c */

Ch = getche ();/* read a character explicitly from the keyboard and send it to the character variable ch */

Putchar (c);/* output this character */

Putchar (ch );

}

6.2 getchar () function: enter a character from the terminal. The getchar function inputs space characters, tabs, and linefeeds as valid characters.

 

Sample Code:

 

 

# Include "stdio. h"

Main ()

{Char c1, c2;

C1 = getchar ();

C2 = getchar ();

Putchar (c1 );

Putchar (c2 );

}

7. Sequential Programming

 

Example 1: Calculate the root of a quadratic equation.

 

Code:

 

 

# Include "math. h"

Main ()

{

Double a, B, c;/* declaring coefficient */

Double x1, x2, p;

Printf ("pleaseinputa, B, c :");

Scanf ("% lf", & a, & B, & c);/* input coefficient */

Printf ("\ n ");

P = B * B-4 * a * c;/* p stores the Discriminant Value */

X1 = (-B + sqrt (p)/(2 * a);/* calculate the root of the equation */

X2 = (-B-sqrt (p)/(2 * );

Printf ("x1 = % f, x2 = % f \ n", x1, x2);/* output result */

}

Example 2: two integers in reverse order.

 

Code:

 

 

# Include <stdio. h>

Main ()

{

Int m, n;

Printf ("inputm (10-99 ):");

Scanf ("% d", & m );

Printf ("\ n ");

N = m % 10;

M = n * 10 + m/10;

Printf ("m = % d \ n", m );

}

 

 

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