C语言英文版教学课件

1、Introduction to Computer(C Programming)Software College , Northeastern University2007,9Chapter3 Operators and Expressions 第1页，共36页。3.1 introduction C operators can be classified into a number of categories. They include: Arithmetic operators. Relational operators. Logical operators. Assignment opera

2、tors. Increment and decrement operators. Conditional operators. Bitwise operators. Special operators.第2页，共36页。3.2 Arithmetic operators Operator Meaning Addition or unary plus Subtraction or unary minus Multiplication Division Modulo division Examples:a-b, a+b, a*b, a/b, a%b第3页，共36页。Example 3.1The Pr

3、ogram shows the use of integer arithmetic to convert a given number of days into months and days.main()int months, days; printf(“Enter daysn”); scanf(“%d”, &days); months = days/30; days = days % 30; printf(“Months=%d days=%d”, months, days);OutputEnter days265Months=8 Days=25Enter days364Months=12

4、Days=4Enter days45Months=1 Days=15第4页，共36页。3.3 Relational OperatorsC supports six relational operators in all: Operators Meaning is less than is greater than = is greater than or equal to = is equal to != is not equal toExample4.5=10 4.5=010 is complement of = = = is complement of !=We can simplify

5、an expression involving the not and the less than operators using the complements as shown below: Actual one Simplified one !(x=y !(xy) x=y !(x!=y) x=y !(xy !(x=y) x 55 & salary 1000) 2. if (number 1000) 第8页，共36页。3.5 Assignment OperatorsC has a set of shorthand operators of the form: v op =exp; wher

6、e v is a variable, exp is an expression op is a C binary arithmetic operator op= is known as the shorthand assignment operator v op =exp; is equivalent to v =v op (exp);Examples: x+=y+1; is equivalent to x=x+(y+1); x+=3; is equivalent to x=x+3;第9页，共36页。Shorthand Assignment Operators Statement with s

7、imple Statement with assignment operator shorthand operator a = a + 1 a += 1 a = a 1 a -= 1 a = a * (n+1) a *= n+1 a = a / (n+1) a /= n+1 a = a % b a %= b第10页，共36页。The use of shorthand assignment operators has three advantages:What appears on the left-hand side need not be repeated and therefore it

8、becomes easier to write.The statement is more concise and easier to readThe statement is more efficientExample: value(5*j-2) = value(5*j-2) + delta; With the help of the += operator, this can be written as follows: value(5*j-2) += delta;第11页，共36页。Example 3.2The Program prints a sequence of squares o

9、f numbers. Note the use of the shorthand operator *=.#define N 100#define A 2main()int a; a = A; while(a b) ? a : b; if (a b) x = a; else x = b;第15页，共36页。3.8 Bitwise OperatorC has a distinction of supporting special operators known as bitwise operators for manipulation of data at bit level. These op

10、erators are used for testing the bits, or shifting them right or left. Bitwise operators may not applied to float or double. Operator Meaning & bitwise AND | bitwise OR bitwise exclusive OR shift right第16页，共36页。3.9 Special OperatorsPointer Operators: & and *Member Selection Operators: . and -第17页，共3

11、6页。The Comma Operator: can be used to link the related expression together. A comma-linked list of expressions are evaluated left to right and the value of right-most expression is the value of the combined expression.Example: value = (x = 10, y = 5, x + y); value = 15;Some applications of comma ope

12、rator are: In for loops: for ( n = 1, m = 10, n d)?1:0);printf(“%dn”, (cd)?1:0);Output a=16 b=10 c=6 a=16 b=11 d=26 a/b = 1 a%b = 5 a*=b =176 0 1第20页，共36页。An arithmetic expression of variables, constants, and operators arranged as per the syntax of the language. The complex mathematical expressions

13、are expressed by C expressions as follows: Algebraic expression C expression a * b c (m+n) * (x+y) a * b / c 3 * x * x + 2 * x + 1 x / y + c 3.10 Arithmetic Expressions第21页，共36页。3.11 Evaluation of ExpressionsExpressions are evaluated using an assignment statement of the form variable = expression; V

14、ariable is any C variable name. When the statement is encountered first and the result then replaces the previous value of the variable on the left-hand side. All variables used in the expression must be assigned values before evaluation is attempted.Example x = a * b c; y = b / c * a; z = a b / c +

15、 d;第22页，共36页。Example 3.4The program illustrates the use of variables in expressions and their evaluation.main()float a, b, c, x, y, z; a = 9; b = 12; c = 3; x = a b / 3 + c * 2 - 1; y = a b / (3 + c) * (2 - 1); z = a (b / (3 + c) * 2) 1;printf(“x=%fn”,x); printf(“y=%fn”,y); printf(“z=%fn”,z);Output

16、x=10.000000 y=7.000000 z=4.000000第23页，共36页。3.12 Precedence of Arithmetic OperatorsAn arithmetic expression without parentheses will be evaluated from left to right using the rules of precedence of operators.Examplex = a-b/3+c*2-1When a = 9, b = 12, and c = 3 x = 9-12/3+3*2-1;第24页，共36页。Rules for Eval

17、uation of ExpressionFirst, parenthesized sub expression from left to right are evaluated.If parentheses are nested, the evaluation begins with the innermost sub-expression.The precedence rule is applied in determining the order of application of operators in evaluation sub-expressions.The associativ

18、ity rule is applied when two or more operators of the same precedence level appear in a sub-expression.Arithmetic expressions are evaluated from left to right using the rules of precedence.When parentheses are used, the expressions within parentheses assume highest priority.第25页，共36页。3.13 Some Compu

19、tational ProblemsApproximate values for real numbersa = 1.0 / 3.0;b = a * 3.0;Division by zeroAvoid overflow or underflow errors第26页，共36页。Example 3.5The program shows round-off errors that can occur in computation of floating point numbers.main()float sum, n, term; int count = 1; sum = 0; printf(“En

20、ter value of nn”);scanf(“%f”,&n); term = 1.0/n; while( count = n)sum = sum +term;count+; printf(“Sum = %fn”, sum);Output Enter value of n 99 Sum = 1.000001 Enter value of n 143 Sum = 0.999999第27页，共36页。3.14 Type Conversions in ExpressionsImplicit Type ConversionC permits mixing of constants and varia

21、bles of different types in an expression. C automatically converts any intermediate values to the proper type so that the expression can be evaluated without loosing any significance. This automatic conversion is known as implicit type conversion.第28页，共36页。int i,x,y;float f;double d;long int l; x =

22、l / i + i * f - d longlongfloatfloatfloatfloatdoubledoubleint第29页，共36页。Conversion HierarchyNote that, C uses the rule that, in all expressions except assignments, any implicit type conversions are made from a lower size type to a higher size type as shown below:shortcharint unsigned int long int uns

23、igned long intfloatdoublelong doubleConversionHierarchy第30页，共36页。Explicit ConversionThe general form of a cast is :(type-name) expressionWhere type-name is one of the standard C data types. The expression may be a constant, variable or an expression. Examplesx = (int) 7.5 a = (int) 21.3/(int)4.5b =

24、(doublt)sum/ny = (int)(a+b)z = (int)a+bp = cos(double)x) 第31页，共36页。Example 3.6The program shows how to use a cast to evaluate the equation sum = (1/i)main()float sum;int n; sum = 0;for( n=1; n=10; +n)sum = sum +1/(float)n;printf(“%2d %6.4fn”, n, sum); Output 1 1.0000 2 1.5000 3 1.8333 4 2.0833 5 2.2833 6 2.4500 7 2.5929 8 2.7179 9 2.8290 10 2.9290第32页，共36页。3.15 Operator Precedence and AssociativityEach operator in C has a precedence associated with it. This precedence is used to determine how an expression involving more than one ope