Lu02a-TypesContantsVariables

• consist of letters, numbers, underlines – in other words, alphanumeric and underscore – [A-Z], [a-z], [0-9], _
• case sensitive • DO NOT begin with a number – first character must be letter or underscore • Choose sensible names! – Direct Viewing. You know the meaning when you see it!
– System predefined: e.g. main, scanf, printf,… – User defined: e.g. name of functions or variables
• Operators:
• • • • • arithmetic operators, relational and logical operators, increment and decrement operators, bitwise operators, assignment operators
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2.3 Data Types
• • Why data need to be distinguished by types? Different type shows different:
– – – – data representations legal numeric area size of storage in memory operations to participate
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2.4 Constants
• Keep “ the variables” in a fixed type and value • A value that will not be changed – Numeric Constants • Integer constant • Real constant • Character constant • String constant – Enumeration – Macro constant – const keyword
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int long
floating point
float double
2.3.1 Basic Types
• int
– an integer, typically reflecting the natural size of integers on the host machine – Usually be stored in 4 bytes of memory in most of computers
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2.4.1 Integer Constant
• integer constant
– 18、-31
• long integer constant
– 123l、123L、123456l、123456L
• unsigned integer constant
– 、 123U
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2.4.2 Real Constant
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2.1 a simple code of C
#include <stdio.h> /* function：Compute the sum of 2 integers input：integer of a and b output/return value： sum of a and b */ int Add(int a, int b) { return (a + b); } /*main function*/ main() { int x, y, sum = 0; printf("Input two integers:"); scanf("%d%d", &x, &y); /*input x and y in form of integer */ sum = Add(x, y); /*invocation of Add function */ printf("sum = %d\n", sum); /*out put the sum of x and y */ }
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sizeof() function
• Can use to find out the size of a given data type (or variable) for your machine:
• Useful when managing data dynamically
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2.3.3 Name an identifier ----variable, function
• int default to signed format (+/- positive/negative)
– 2‟s complement – Most significant bit (MSB) is sign(+/- positive/negative) – Can also use unsigned int
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Summary of Data types
• Integer – long integer – short integer • Float • Double • Long double • Character – no string type – construct as array of chars
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2.2 C Symbols
• Separators:Space;Return/newline;Comma;etc. • Other symbols – “{”&“}” • indicate the region of a function or a block • used in pair – “/*”&“*/” • for comments, used in pair • Data: – Variables; – Constants
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2.3.4 Storage of Basic Data Types
• Unlike Java, size is machine-dependent!
• Programs can be non-portable unless careful
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Other Variants of Data Types
• Be considered as double by default
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2.4.3 Character constant
• Single character are enclosed in single quotes
– ‟a‟，‟A‟，‟5‟，‟%‟，‟$‟…… – There can be only one character within single quotes, except with the "\" at the beginning – It is a common integer. May be involved in various arithmetic calculation. – Each character corresponds to a value between 0 and 255， refer to ASCII Table – attention：‟5‟ and int 5 are not the same
Chapter02 Types, Constants and Variables
Lecturer: Dr. JING LU
Jing.lu@
In this lecture we will
• Look at basic syntactic and semantic elements of C – Data types and declarations – Arithmetic operators, including their order of precedence – Arithmetic expressions
一个简单的C程序例子
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2.2 C Symbols
• Keywords: auto, break, char, do, else, float, goto, if, long,
return, sizeof, typedef, union, void, while……
• Identifiers:Variable, Constant, Function, etc
• Namely, floating point constant
– Decimal form: 123.45, 456.78 – Exponential form: 1e-2, 4.5e3 – Single-precision real constants: 123.45f, 456.78F, 1e-2f, 4.5e3F – Long double constants: 123.45l, 456.78L, 1e-2l, 4.5e3L
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2.3.3 Name an identifier ----variable, function
• DO NOT use keyword to name an identifier
– int, float, for, while, if, etc.
• Use prefix to customize:
• Some de facto variable names and function names
– e.g. the loop indicators of for statement are i, j, or k – Underscore as first character is usually reserved for system functions