C study notes[2]

文章目录

• integer
• input
• constant
• references

integer

1. the format character %d in the printf funtion indicates to output with integer format In decimal form. if the integer bases 8 which is octal or bases 16 which is hexadecimal,you should use the %o or %x.we can create the prefix such as 0 or 0X when adding # to those format character.

# include <stdio.h>
int main(void) {
	int x = 9;
	printf("%o,%#o,%d,%x,%#x",x,x,x,x,x);
}

2. the char type is a fantastic data type which take up 8 bits ,to occupy one byte memory of computer for achieving some tasks such as representing as a small integer less than 256,a set of binary explaining a instruction, a character for ASCII,a byte's slice of datas from a file and so on.

3. In C, non-printing characters (also called control characters) are characters that do not represent a written symbol but instead control formatting, transmission, or other functions.

4. Common Non-Printing Characters in C

Escape Sequence	ASCII Value	Description
\a	0x07	Alert (bell)
\b	0x08	Backspace
\t	0x09	Horizontal tab
\n	0x0A	Newline (line feed)
\v	0x0B	Vertical tab
\f	0x0C	Form feed (page break)
\r	0x0D	Carriage return
\0	0x00	Null character (string terminator)
\\	0x5C	Backslash (printing, but escaped)
\'	0x27	Single quote
\"	0x22	Double quote

• Hexadecimal : \x1B (escape character)
• Octal : \033 (same escape character)

printf("Hello\tWorld!\n");      // Uses tab and newline
printf("Alert: \a\n");          // Triggers a beep (if supported)
printf("Back\bspace\n");        // Prints "Backspace" after backspace
printf("Null terminator: \0\n"); // Stops string at \0
printf("Hex: \x41\n");  // Prints 'A' (ASCII 0x41)
printf("Octal: \101\n"); // Also prints 'A' (octal 101)

5. _Bool is a Boolean data type introduced in the C99 standard to represent true/false values. It can store either 1 (true) or 0 (false).

#include <stdio.h>
#include <stdbool.h> // For bool, true, false

int main() {
    _Bool isTrue = 1;   // Works, but not recommended (use bool instead)
    bool isFalse = false; // Preferred (via <stdbool.h>)
    
    printf("isTrue: %d\n", isTrue);   // Output: 1
    printf("isFalse: %d\n", isFalse); // Output: 0
    
    return 0;
}

input

1. scanf function used to receive user's input with character format such as %s,%d and so on,as similar as format character parameter of printf function.

• Common format specifiers for scanf:

  %d - integer

  %f - float

  %lf - double

  %c - single character

  %s - string (whitespace delimited)

  %x - hexadecimal integer

  %o - octal integer

int age;
float height;
printf("Enter your age and height: ");
scanf("%d %f", &age, &height);

you also declare a char array ,50 bytes in size,for inputing a set of chars maximized 50 used in scanf function.

every char array substantially is a sequence consisted of a lot of chars,can be called as character string in C language,capacity of a char array is its length-1 because of ending with \0(Null character) .

char name[50];
printf("Enter your name: ");
scanf("%49s", name);  // limit input to prevent buffer overflow

string "a" and char 'a' are different that "a" include Null and 'a' only occupy one byte.

2. scanf return an integer indenfied the amount of reading chars sucessfully.
3. The asterisk (*) in scanf has a special meaning - it's called an "assignment suppression character".

int x;
scanf("%*d %d", &x);  // Reads but discards first integer, stores second in x

the format character flaged as * will be omitted to input.

4. In printf, * is used for dynamic field width and precision specification.

int width = 10;
int num = 42;
printf("%*d", width, num);  // Prints num in 10-character width
int precision = 3;
float pi = 3.14159;
printf("%.*f", precision, pi);  // Prints "3.142"

int width = 8;
int precision = 2;
float value = 123.4567;
printf("%*.*f", width, precision, value);  // Prints "  123.46"

constant

1. declare a constant can use # define constantname value ,for example, #define x 0.001.
2. const is a keyword used to declare variables as read-only (constant).

#include <stdio.h>

int main() {
    const int c = 10;  // 'c' is a constant integer
    // c = 20;  // ERROR: Cannot modify a const variable
    printf("c = %d\n", c);  // Output: c = 10
    return 0;
}

3. Predefined Symbolic Constants,these come built-in with the C language or standard libraries:

   Standard Library Constants (from headers like <limits.h>, <float.h>, <math.h> etc.):

  NULL (null pointer)

    EOF (end-of-file)

    BUFSIZ (standard buffer size)

    FLT_MAX (maximum float value)

    INT_MAX (maximum integer value)

references

1. deepseek