C language - characters and strings, arithmetic operators, type conversions

Catalog

One 、 Characters and strings

1. character

2.ASCII Character table

3. character string

Two 、 Arithmetic operator

1. What is the purpose ？

2. expression

3. Precedence and associativity of operators

4. Type conversion  

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One 、 Characters and strings

1. character

• Character variables can be used to store integers

The code for ：

#include <stdio.h>

int main()
{
	char a = 'C';
	
	printf("%c = %d\n", a, a);
	
	return 0;
	
}

Running results ：

2.ASCII Character table

        ASClI（American Standard Code for Information Interchange, American standard information exchange code ） It's a computer coding system based on the Latin alphabet , Mainly used to show modern English and other western European languages . It's the most common single byte encoding system today , And equivalent to international standards ISO/IEC646.
        standard ASCⅡ Character table usage 7 Bit binary number to represent all upper and lower case letters , Numbers 0 To 9、 Punctuation , And special control characters used in American English .

• ASCIl Numbers on the character table 0~31 as well as 127（ common 33 individual ） Assigned to the control character , It's used to control peripheral devices like printers .
• ASCIl Numbers on the character table 32~126 Assigned to characters that can be found on the keyboard , Appears when you view or print a document

The code for ：

#include <stdio.h>

int main()
{
	char a = 70, b = 105, c = 115, d = 104, e = 67;
	
	printf("%c%c%c%c%c\n", a, b, c, d, e);
	
	return 0;
}

Running results ：

  Conclusion ： The character type is a special integer . But for integers , If don't write signed or unsigned, The system default is signed; But for character types ,C Language and There's no rule The default is signed still unsigned, At the discretion of the compiling system .

The code for ：

#include <stdio.h>

int main()
{
	unsigned char height;
	
	height = 170;
	
	printf(" His height is %d centimeter ！\n", height);
	
	return 0;
}

Running results ：

  If not add “unsigned”, The result is ：

so , If use char To store height , You must add “unsigned”.

3. character string

• Syntax for declaring strings ：char Variable name [ Number ];
• Get the space of each variable through the index number ： Variable name [ Reference no. ] = character ;

example ：

• Declaration string ：char name[2];
• Assign a value to a string ：name[0] = 'F';   name[1] = 'i';
• Define string ：char name[5] = {'F', 'I', 'S', 'H', 'c'};

The code for ：

#include <stdio.h>

int main()
{
	char a[4] = {'L', 'O', 'V', 'E'};
	printf("%s\n",a);
	return 0;
}

Running results ：

  There seems to be no problem with this result , But if you print another （ such as hello）, Then there will be confusion . This is because , To determine the end position of the string in memory ,C The language stipulates adding a... At the end of the string “\0” To indicate the end .

Modify the above code as follows ：

char a[5] = {'L', 'O', 'V', 'E', '\0'};

You can also write a pair directly “[]”, as follows ：

char a[] = {'L', 'O', 'V', 'E', '\0'};

Or write string constants directly , Use double quotation marks , There is no need to add “\0”. as follows ：

char a[] = {"LOVE"};

  If you use string constants , You can also remove the braces . as follows ：

char a[] = "LOVE";

Two 、 Arithmetic operator

C Language supports us to process data by providing operators .

1. What is the purpose ？

The operands that operators act on are called operands , Whether an operator is binocular or unary depends on how many operands it has , How many operands work .

 C Language has a unique ternary operator , It has 3 Operands , The following will be supplemented .

2. expression

An expression that connects operands with operators and parentheses , It's called an expression .

Such as ：1 + 1; 'a' + 'b';  a + b;  a + 'b' + pow(a,b) * 3 / 4 + 5

3. Precedence and associativity of operators

Plus operator 、 Negative operator   >  /、*、%   >  +、-  

The code for ：

#include <stdio.h>
#include <math.h>

int main()
{
	int i,j,k;
	
	i = 1 + 2;
	j = 1 + 2 * 3;
	k = i + j + -1 + pow(2,3);//3 + 7 + (-1) + 8 
	
	printf("i = %d\n",i);
	printf("j = %d\n",j);
	printf("k = %d\n",k);
	
	return 0; 
}

Running results ：

4. Type conversion  

Type conversion is to ensure the accuracy of calculation .

The code for ：

#include <stdio.h>

int main()
{
	printf(" Integer output ：%d\n", 1 + 2.0);
	printf(" Floating point output ：%f\n", 1 + 2.0);
}

Running results ：

  so , Integer output is the wrong result , This is because ,1 + 2.0 The result of automatic conversion is 1.0 + 2.0, Is a floating-point number , If a floating-point number is forcibly changed to an integer number, the output will print the wrong result .

C Language allows us to cast data types of operands , Precede the operand with （） Just enclose the target data type . as follows ：

#include <stdio.h>

int main()
{
	printf(" Integer output ：%d\n", 1 + (int)2.0);
	printf(" Floating point output ：%f\n", 1 + 2.0);
}

Running results ：

  If the 2.0 Change it to 1.8, The result is ：

  If the 2.0 Change it to （1 + 0.8）, The result is ：