ECE209_Lecture_03.pdf

Lecture 3: More on operators and expressions ECE 209 January 20, 2010 ECE 209: Computer Systems Programming Tuck Assignments ?HW0 -- Due 3/28 ?HW1 -- Due 1/25 ?CodeLab ? Ch 2,3 -- Jan 25 ?Reading: ? PP: Ch 12, C: 2,3,5 ? For next time: PP: 13, C: 6 2 ECE 209: Computer Systems Programming Tuck Types of data ?More about types ? char = signed character, at least 8 bits (usually assumed to be 1 byte) ? ASCII character: ?A? -- place one character in single quotes (**preferred coding) ? Decimal value: 65 ? Octal ASCII value: ?\0101? ? Hexadecimal ASCII value: ?\x41? ? Also other special characters: ?\n? -- newline, ?\t? -- tab 3 ECE 209: Computer Systems Programming Tuck Types of data ?More about types ? double (or float) = signed floating point ? Decimal: 1.23 ? Scientific: 1.0e23 , which means 1.0 x 10 23 ? Other Examples ? 2.0E20 ? 3.4e-9 ? -1. ? .23 ? 3.14159e0 4 ECE 209: Computer Systems Programming Tuck Excercise ?Declare a variable to hold Avogadro?s number. 5 ECE 209: Computer Systems Programming Tuck Printing other types #include int main(void) { int days_in_a_week = 7; double avocado = 6.02e23; char initial = ?T?; /* need a different escape code for each type so that printf knows how to treat it */ printf(?days in a week = %d\n?, days_in_a_week); printf(?Avocado?s Number = %e\n?, avocado); printf(?My last initial = %c\n?, initial); return 0; /* exit the program */ } 6 ECE 209: Computer Systems Programming Tuck Operators ?C provides operators to manipulate variables of all types (unless specified otherwise) ? Assignment ? Arithmetic operations: addition, subtraction, multplication, division, etc. ? Logical operations: and, or, negation ? Bitwise operators: and, or, xor, inversion ? Parenthesis to group operations ? Relational operators: less than, greater than, equal, not equal 7 ECE 209: Computer Systems Programming Tuck Operators --- actions to be performed on data ?Assignment: lvalue = rvalue ? Rvalue: the right side of an assigment, it can be any value ? Lvalue: must be a variable (is associated with a memory location) ? After the operation, Lvalue is equivalent to rvalue x = 100; y = 5; x = y * 2; /* after this statement, x contains 10 */ 8 ECE 209: Computer Systems Programming Tuck Arithmetic operators ?Binary arithmetic operations: +, -, *, /, % ? Addition: + ? Subtraction: - ? Division: / ? For integers, it throws away the remainder: 7/3 = 2 ? For floats, 7/3 = 2.333... ? Modulo: % ? Computes the remainder and is only available for int and char ? If mixed types are in a C operation, smaller precision is promoted to larger precision (e.g. int is converted to float, char is promoted to int) 9 ECE 209: Computer Systems Programming Tuck Arithmetic operators ?Unary operators ? + : positive ? - : negative 10 ECE 209: Computer Systems Programming Tuck C Expressions ?An expression can be one of the following things in C ? a variable ? a value (literal) ? an operation on values or variables or both ? a function call ? an operation on expressions (yes, this is a recursive definition) ? Important: An expression is NOT a statement ? But, you can add a semicolon to any expression to create a statement 11 ECE 209: Computer Systems Programming Tuck More on expressions ?Which of the following are expressions, and if so, what are their types? printf(?I?m an expression?) 0+1 ?A?; ?A? * 3 x = 3.5e4-.5; 12 ECE 209: Computer Systems Programming Tuck How to interpret an expression ?What does this expression evaluate to: 2 + 3 - 4 + 5 13 ECE 209: Computer Systems Programming Tuck Operator precedence ?Precedence determines the order operators are evaluated ? I.e. it answers the question: where are the implicit parentheses? ? Provides a rigorous way for programmer & compiler to agree on the meaning ?Precedence becomes more important as we learn more operators ? For arithmetic operations precedence works as you expect (from algebra) 14 ECE 209: Computer Systems Programming Tuck Precedence table 15 Operators Associativity () Left to Right + - (Unary) Right to Left * / Left to Right + - (Binary) Left to Right = Right to Left Highest Precedence (Apply first) Lowest Precedence (Apply last) ECE 209: Computer Systems Programming Tuck Example a + b - c + d 16 ECE 209: Computer Systems Programming Tuck Example y = 6 * 12 + 5 * 20 + 1 17 ECE 209: Computer Systems Programming Tuck Example x = y = x + y 18 James Tuck ECE209_Lecture3.key