C++ Expressions and Arithmetic Operations

Expressions An expression is a portion of a C++ statement that performs an evaluation of some kind Generally requires that a computation or data manipulation be performed to produce a result of a specified type Arithmetic expression Performs a numeric computation producing a numerical result Logical expression Produces a Boolean result evaluating to true or false String expression Produces a result of type string Expressions may contain other expressions which are evaluated in order producing an overall result Professor John Carelli Kutztown University Computer Science Department

Arithmetic Expressions Basic arithmetic operations + Addition - Subtraction * Multiplication / Division % Modulus (remainder operator) integers only! Each is a binary operator Operate on 2 numbers, left and right Examples: 2+2 4/2 2*5 Professor John Carelli Kutztown University Computer Science Department

Integer Division The result is always an integer!!! Any remainder (or fraction) gets truncated NOT rounded! Examples: o 15 / 3 is 5 o 15 / 2 is 7 o 0 / 15 is 0 o 15 / 0 is undefined To get decimals, use floating point numbers 15.0 / 2.0 -> 7.5 Professor John Carelli Kutztown University Computer Science Department

Modulus for Integers Used only with integers Get a compiler error if used with a float Yields remainder instead of quotient the result is integer Examples: o 7 % 2 -> 1 o 299 % 100 -> 99 o 49 % 5 -> 4 o 15 % 0 undefined o 15 % -7 system dependent Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Increment and Decrement Increment ++ Increment adds one to an existing variable: x++ If x was 2, it becomes 3 post-increment Can also use ++x (pre-increment) Decrement -- Decrement subtracts one from an existing variable: x-- If x was 2, it becomes 1 post-decrement Can also use --x (pre-decrement) Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Mixed-type Expressions Example: 4.6 / 2 evaluates to 2.3 Rule: when an integer and a floating point operand are combined by an operator, the integer gets converted to the floating point type Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Assignment (= =) The value of a variable can be set using the assignment operator (=) It is NOT an equals operator Examples: x= 3 +5; y= x/2; Also: y= 3*y; Note: This is NOT saying that y is equal to 3*y (which would not make much sense). It is multiplying y by 3 and assigning the result back to y. Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Mixed-type Assignments If the variable on left side of assignment is of different type than the type of the evaluated expression on the right side of =, the result of the expression must be converted to the appropriate type Conversion from a float to an int involves dropping (i.e. truncating, not rounding!) the decimal part Example: int n; float x=2.7; n= x; // n will be assigned the value 2 (trick: to round, add 0.5 first!) Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Mixed-type Assignment Examples float a, b, x; int m, n; a=10; b = 3.5; m=5; n = 10; x = m / n; // result is 0 assigned to x m = b * 3; // result is 10 assigned to m // result is 10.0 stored in a Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Casting Type casting allows for explicit conversion from one data type to another Accomplish by using the type name directly int sum=10, n=4; float average= float(sum) / float(n); result is: 2.5 (not 2!) Professor John Carelli Kutztown University Computer Science Department

Order of Operator Precedence Highest ( ) nested expressions evaluated inside out unary +, - *, /, % binary +, - Associativity Lowest Warning: watch out for the types of operands and the type of the result when evaluating each operand! Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

PEMDAS Order of operations: 1. Parentheses: () 2. Unary Negation (-) also increment (++) and decrement (--) 3. Exponentiation: x2 (not in C++) 4. Multiplication (*) or Division (/) - also Modulus (%) 5. Addition (+) or Subtraction (-) If operations are at the same level, they are evaluated left to right Except for unary operations which go right to left Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Step-by-Step Expression Evaluation float area, PI=3.14159, radius; radius= 2.0; Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Step-by-Step Expression Evaluation: z z - - (a +b / 2) + w * (a +b / 2) + w * - -y y Note: all variables are type int Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Evaluation tree for: m = x + k / 2; m = x + k / 2; int m, k=5; float x=5.5; Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Mathematical Formulas in C++ a = bc not valid C++ syntax! Must use * operator a = b * c; m =y b x a Must use ( ) and / m = (y - b) / (x - a); . why? Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Pre Pre vs vs. . Post Increment and Decrement Post Increment and Decrement Pre-increment operations occur before the rest of the expression is evaluated Do the increment first, then use that result in the remaining expression Pre-increment: int x=2, y; y =1 + ++x; Result: x: 3 y: 4 Post-increment operations occur after the rest of the expression is evaluated Evaluate the expression first with the initial value of the variable to be incremented. Then, do the incrementation on the variable. Same applies to decrement Post-increment: int x=2, y; y =1 + x++; Result: x: 3 y: 3 Professor John Carelli, Kutztown University Source: Pearson Education, Inc. Publishing as Pearson Addison-Wesley