Section 17 Assignment Operators and Expressions

1. Simple assignment expression

#include <stdio.h>
#include <math.h>
int main()
{
    
    
	int a, b;
	a = 3;
	double c, d;
	b = a * a;
	c = 3.75;
	d = sin(b) + 1;
}

2. Automatic conversion of data type during assignment

Left value	Right value	Conversion method	For example
Integer variable	Floating point data	Floating point numbers discard the decimal part	int a=4.38;
Floating-point variable	Integer data	The value is unchanged and stored in exponential form	double=375;
float variable	double data	Decreased accuracy, possible overflow	float f=2.8e59
unsigned variable	Signed data of the same length	Copy as it is, but the original sign bit is also treated as the value part	unsigned int u=-32765;

#include <stdio.h>
int main()
{
    
    
	int i = 3.123456789;
	double d = 3;
	float f = 3.123456789123456789;
	unsigned u1 = 1234;
	unsigned u2 = -1234;
	printf("i=%d\n", i);
	printf("d=%f\n", d);
	printf("f=%f\n", f);
	printf("u1=%u\n", u1);
	printf("u2=%u\n", u2);
}
输出结果及解析:
i=3           /舍弃小数部分
d=3.000000    /整数转为小数存储和输出
f=3.123457    /精度降低
u1=1234       /值未变
u2=4294966062 /符号位当数值处理

Three. Compound assignment operator

#include <stdio.h>
int main()
{
    
    
	int a = 9;
	a += 3; printf("%d\n", a); a = 9;
	a -= 3; printf("%d\n", a); a = 9;
	a *= 3; printf("%d\n", a); a = 9;
	a /= 3; printf("%d\n", a); a = 9;
	a %= 3; printf("%d\n", a); a = 9;
}
输出结果:
12
6
27
3
0

Advantages of compound assignment operator
① simplify the program
② improve efficiency
4. Assignment expression and its value
Assignment statement:
a=3;
b+=6.32;
assignment expression:
a=3
b+=6.32

 #include <stdio.h>
int main()
{
    
    
	int a, b, c;
	printf("%d\n", (a = 5));
	printf("%d\n", (b = (c = 6)));
	printf("%d %d %d\n", a, b, c);
}
5
6
5 6 6

Five. Assignment expression evaluation

Combination method: from right to left

a=(b=5)
a=b=c=5
a=5+(c=6)
a%=(n%=2)
printf("%d",(j=i++）);
(a=3*5)=4*3
a+=a-=a*a

6. Click self-test

Section 17 Assignment Operators and Expressions

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