c語言基礎(chǔ)教程課件(英文版)ch(4)(已修改)
2025-01-24 07:57 本頁面
【正文】 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 Study: 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 sign 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 = 。 length = 。 A First Book of ANSI C, Fourth Edition 5 Assignment (continued) ? 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 * 。 ? The value of the expression to the right of = is puted first and then the calculated value is stored in the variable to the left of = ? Variables used 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 puter uses the value that happens to occupy that memory space previously (piler 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 ? Multiple assignments are possible in the same statement a = b = c = 25。 ? All = operators have the same precedence ? Operator has righttoleft 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 ? The automatic conversion across an assignment operator is called an implicit type conversion int answer。 answer = 。 // is converted to 2 – Here the implicit conversion is from a higher precision to a lower precision data type。 the piler will issue a warning A First Book of ANSI C, Fourth Edition 9 Explicit Type 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 truncating s
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