programming in ANSI C-Chapter 3 Operators and Expressions

1、Chapter 3Operators and Expressions,PROGRAMMING IN ANSI C,Operators,Expressions,An expression is a sequence of operands and operators that produces a single value. This value may be any data type except void.,How to learn operators and expressions?,When we study operators and expressions, we must pay

2、 attention to such 5 points: The function of operators. The relation of operators and operands: How many operands does the operator need? Which types does the operator require? The precedence of the operator. The associativity of the operator. The type of the calculated result.,Arithmetic Operators

3、C doesnt supply exponential operator, so you can write some multiplication, or you can use mathematic function pow(x,y) in the C function library to express xy; Notice the precedence of those arithmetic operators, and you should reasonably use parentheses.,Arithmetic Operators b = a * 3.0; Dont make

4、 any expression divide zero. Avoid data overflow.,Relational Operators a b c = a b a b f = a b c,32，the value is 1 1=1， the value is 1 b+c=3， the value is 0 d=1 ab is 1，1c is 0，so: f = 0,Relational Operators a = b = a;/* a = 0 */,Logical Operators !a aint a = b = 5;Wrong!int a = 5, b = 5;Right!,Assi

5、gnment Operators a = b = c = 5; a = 5 + (c=6); a = (b=4) + (c=6);, c = 5, b = c, a = b /*a=5, b=5, c=5*/ c = 6, a = 5+c /*a=11, c=6*/ b = 4, c = 6, a = b+c /*a=10, b=4, c=6*/,Assignment Operators is equivalent to:variable = variable op expression e.g.x * = y + 1; is equivalent to:x = x * (y + 1);,As

6、signment Operators a += a -= a*a ;, a += a = 4 a += (a = a 4) a += (a = -2) a += a a = a + a a = (-2) + (-2) a = -4,Increment and Decrement Operators,+- m +; or + m; is equivalent to: m = m + 1; m -; or - m; is equivalent to: m = m - 1; Precedence ： same as unary +, unary -, ! Associativity： Right t

7、o left,(10 / m) + Wrong! 10 / m + Right!,Increment and Decrement Operators,int m=5, n; n = 10 / m+; is equivalent to: n = 10/m; m+; n = 10 / +m; is equivalent to: +m;n = 10/m;,Increment and Decrement Operators,j=3; k=+j; j=3; k=j+; j=3; printf(%d,+j); j=3; printf(%d,j+); a=3;b=5;c=(+a)*b; a=3;b=5;c=

8、(a+)*b;,j=j+1; k=j; result：k=4, j=4 k=j; j=j+1; result ：k=3, j=4 j=j+1; printf(); output:4 printf(); j=j+1; output:3 a=a+1; c=a*b; result ：a=4，c=20 c=a*b; a=a+1; result ：a=4，c=15,Increment and Decrement Operators,Notice The operand of + or - must be a variable and not any expression or any constant.

9、,Comma Operator b = (a = 3*4, 5*2) ; a=1; b=2; c=3; printf(%d,%d,%d, a, b, c); printf(%d,%d,%d, (a, b, c), b, c);,a = 12 a = 12, b = 10 output: 1, 2, 3 output: 3, 2, 3,Implicit Type Conversion,The rules of conversion: P67In all expressions except assignments, any implicit type conversions are made f

10、rom a lower size type to a higher size type as shown here:,Implicit Type Conversion,During assignment: If expression is real type and the variable is integer type, the value of expression will be truncated its fractional part. If expression is double type and the variable is float type, the value of

11、 expression will be round its digits. If expression is long type and the variable is int type, the value of expression will be drop its higher byte.,Implicit Type Conversion,int i, x;float f;double d;long L; x = L / i + i * f - d;,long,float,float,float,double,double,double,int,Notice: in the whole

12、process of type conversion, only the type of the interim value used in evaluation is converted, but all the types of variables are not converted. Except the variable “x” assigned a value, all the values of other variables are not changed.,Explicit Type Conversion,Form ：(type-name) expression Precede

13、nce ： same as unary +, unary -, !, +, - Associativity： Right to left e.g. (int) (x+y) (int) x + y,main() float x, y ; x = 3.6 ; y = (int) x * 2 ; printf(x=%.2f, y=%.2f, x, y); ,x=3.60, y=6.00,Notice: like the implicit type conversion, only the type of the interim value used in evaluation is converted, bu