Arithmetic Operators - Introduction to Low Level Programming | CMSC 212, Study notes of Computer Science

Download Arithmetic Operators - Introduction to Low Level Programming | CMSC 212 and more Study notes Computer Science in PDF only on Docsity!

Announcements

z^

Program #1B– Due week from Thursday

z^

Reading– Chapter 5 (today)– Chapter 15 (Thursday)

Arithmetic Operators

+^

Add two numbers

-^

Subtract two numbers

*^

Multiply two numbers

/^

Divide two numbers

For integers, divide truncates to whole number

% Remainder of integer divideAll except % may be used with integers or floats

Bit Shift Operator

z^

C has operators to bit shift numbers– number of bits changed depends on size of variable

z^

Left Shift (number << xxx)– Move each bit of number to the left by xxx bit positions– Leftmost xxx bits discarded– Rightmost xxx bits gets 0

z^

Right Shift (number >> xxx)– Move each bit of number to the right by xxx bit positions– Rightmost xxx bits discarded– Leftmost xxx bits gets 0

or replicate sign bit

• for unsigned gets 0• for signed, its

implementation dependent

Examples of Bit Shift

unsigned int a, b;a = 0x0000 0010;b = a >> 1;

/* b is now 0x0000 0008 */

b = a >> 4;

/* b is now 0x0000 0001 */

b = a >> 5;

/* b is now 0x0000 0000 */

b = a << 1;

/* b is now 0x0000 0020 */

b = a << 4;

/* b is now 0x0000 0100 */

b = a << 5;

/* b is now 0x0000 0200 */

Assignment Operator

z^

Assignment is an operator, not a statement!– x = y + 3;– a = x = y + 3;– assignment is right associative, so

• a = x = y + 3 is the same as a = (x = y + 3)
  • value of assignment operator is result of assignment
    • if truncation is applied, the truncated value is used• Consider:

unsigned char x;unsigned int a, b;b = 0xabcd;a = x = b;at the end, a = 0xcd;

Compound Assignment

z^

Shorthand to combine binary operator and assignment– += add right operand the left operand and update left

• a += 3 is equivalent to a = a + 3
  • Also: -=, *=, /=, %=, <<=, >>=, &=, ^=, |= z^

Handy for complex expressions in LHS– a[ i * 2 + j - f(n)] = a[ i * 2 + j - f(n)] + 3;– a[i * 2 + j - f(n)] += 3;– assumes f(n) has no side effects

Unary Operators (cont.)

z^

& Return the address of a variable– int a, *b;– a = 3;– b = & a;

/* b now points to the location of a */

z^

sizeof - return number of bytes in variable or type– int a;– sizeof int– sizeof(int);– sizeof(a);

z^

() - convert to a new type– int a; float b;– b = (float) a;

Unary Operators (cont.)

z^

++ increment operator– can be prefix or postfix++a - add one to a and use new value as result of expression.a++ - add one to a and use old value as result of expression.

z^

-- decrement operator– can be prefix or postfix--a - subtract one from a and use new value as result of expressiona-- - subtract one from a and use old value as result of expression.Examples:

a = --b + 10;c = ++a;d = b++;

Logical Operators

z^

&& - and– if both operands are non-zero result is 1– else result is 0– uses short-circuit evaluation

• if the first operand is not true, second is not evaluated• if ((a++) && (--b)) { .. }
  • if a is zero at start, a = 1 and b is not changed

z^

|| or– if either operands is non-zero result is 1– else result is 1

z^

Caution: && is not the same as &– & performs a bitwise operation

Other Operators

z^

expr1? expr2 : expr3– if expr1 is non-zero, expr2 is evaluated and is the result– if expr1 is zero, expr3 is evaluated and is the result– a = (2 > 3)? 65 : 0;

z^

Comma– evaluates both operands, rightmost is the result– a = (1,2,3); vs. b = 1,2,3;

• assignment is higher precedence than ,• a ends up 3 and b ends up 1

Precedence

z^

There is a set of rules about precedence of operator– Most important precedence rule:

• When in doubt, put in () to ensure correct order
  • Order (highest to lowest):
    • ()• Function call, subscript, postfix increment/decrement• rest of unary operators• type conversion• Arithmetic operators• Relational operators• Bit operators• Assignment operators• ,