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1、A First Book of ANSI C Fourth Edition,Chapter 3 Processing and Interactive Input,A First Book of ANSI C, Fourth Edition,2,Objectives,Assignment Mathematical Library Functions Interactive Input Formatted Output,A First Book of ANSI C, Fourth Edition,3,Objectives (continued),Symbolic Constants Case St
2、udy: Interactive Input Common Programming and Compiler Errors,A First Book of ANSI C, Fourth Edition,4,Assignment,The general syntax for an assignment statement is variable = operand; The operand to the right of the assignment operator (=) can be a constant, a variable, or an expression The equal si
3、gn in C does not have the same meaning as an equal sign in algebra length=25; is read “length is assigned the value 25” Subsequent assignment statements can be used to change the value assigned to a variable length = 3.7; length = 6.28;,A First Book of ANSI C, Fourth Edition,5,Assignment (continued)
4、,The operand to the right of the equal sign in an assignment statement can be a variable or any valid C expression sum = 3 + 7; product = .05 * 14.6; The value of the expression to the right of = is computed first and then the calculated value is stored in the variable to the left of = Variables use
5、d in the expression to the right of the = must be initialized if the result is to make sense amount + 1892 = 1000 + 10 * 5 is invalid!,A First Book of ANSI C, Fourth Edition,6,Assignment (continued),If width was not initialized, the computer uses the value that happens to occupy that memory space pr
6、eviously (compiler would probably issue a warning),A First Book of ANSI C, Fourth Edition,7,Assignment (continued),= has the lowest precedence of all the binary and unary arithmetic operators introduced in Section 2.4 Multiple assignments are possible in the same statement a = b = c = 25; All = oper
7、ators have the same precedence Operator has right-to-left associativity c = 25; b = c; a = b;,A First Book of ANSI C, Fourth Edition,8,Implicit Type Conversions,Data type conversions take place across assignment operators double result; result = 4; /integer 4 is converted to 4.0 The automatic conver
8、sion across an assignment operator is called an implicit type conversion int answer; answer = 2.764; /2.764 is converted to 2 Here the implicit conversion is from a higher precision to a lower precision data type; the compiler will issue a warning,A First Book of ANSI C, Fourth Edition,9,Explicit Ty
9、pe Conversions (Casts),The operator used to force the conversion of a value to another type is the cast operator (dataType) expression where dataType is the desired data type of the expression following the cast Example: If sum is declared as double sum;, (int) sum is the integer value determined by
10、 truncating sums fractional part,A First Book of ANSI C, Fourth Edition,10,Assignment Variations,sum = sum + 10 is not an equationit is an expression that is evaluated in two major steps,A First Book of ANSI C, Fourth Edition,11,Assignment Variations (continued),A First Book of ANSI C, Fourth Editio
11、n,12,Assignment Variations (continued),A First Book of ANSI C, Fourth Edition,13,Assignment Variations (continued),Assignment expressions like sum = sum + 25 can be written using the following operators: += -= *= /= %= sum = sum + 10 can be written as sum += 10 price *= rate is equivalent to price =
12、 price * rate price *= rate + 1 is equivalent to price = price * (rate + 1),A First Book of ANSI C, Fourth Edition,14,Accumulating,The first statement initializes sum to 0 This removes any previously stored value in sum that would invalidate the final total A previously stored number, if it has not
13、been initialized to a specific and known value, is frequently called a garbage value,A First Book of ANSI C, Fourth Edition,15,Accumulating (continued),A First Book of ANSI C, Fourth Edition,16,Accumulating (continued),A First Book of ANSI C, Fourth Edition,17,Counting,A counting statement is very s
14、imilar to the accumulating statement variable = variable + fixedNumber; Examples: i = i + 1; and m = m + 2; Increment operator (+): variable = variable + 1 can be replaced by variable+ or +variable,A First Book of ANSI C, Fourth Edition,18,Counting (continued),A First Book of ANSI C, Fourth Edition,
15、19,Counting (continued),A First Book of ANSI C, Fourth Edition,20,Counting (continued),When the + operator appears before a variable, it is called a prefix increment operator; when it appears after a variable, it is called postfix increment operator k = +n; is equivalent to n = n + 1; / increment n
16、first k = n; / assign ns value to k k = n+; is equivalent to k = n; / assign ns value to k n = n + 1; / and then increment n,A First Book of ANSI C, Fourth Edition,21,Counting (continued),Prefix decrement operator: the expression k = -n first decrements the value of n by 1 before assigning the value of n to k Postfix decrement operator: the expression k = n- first assigns the current value of n to n and then reduces the value of n by 1,A First Book of ANSI C, Fourth Edition,2
