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APS105

Calculating

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Basic Math Operations

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Basic Arithmetic Operators

• Operators:– Addition: +– Subtraction: -– Multiplication: *– Division: /

• Recall order of operations:– * and / have highest precedence– left to right otherwise

• Speficy grouping/precedence: ( )– Not: { } or [ ]

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Examples

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The Modulo Operator %

• x % y returns the remainder of x / y• has same precedence as / and *• x and y must be ints

– signs of x and y are ignored if either is negative– but result takes the sign of x (is negative if x is)

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Modulo Examples

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Calculating with Char Values

• Recall ‘A’ is encoded in ASCII as decimal 65char letter = ‘A’; // letter = 65

• Since char value is a number can do math.

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Increment and Decrement

• increment: ++– adds one to the variable– AND changes the variable to this new value– i++; // means the same as i = i + 1;

i = 10; i++; // i = 11 afterwards

• decrement: --– subtracts one from the variable– AND changes the variable to this new value– i--; // means the same as i = i - 1;

i = 10; i--; // i = 9 afterwards

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Assignment

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Assignment

• An assignment statement contains an ‘=‘• Evaluation order:

– right-hand-side (RHS) of = is evaluated first– Then assignment of result to left-hand-side (LHS)

• Example: x = 5;

x = x + 2;

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Operation-Assignment

• Some operations can be combined with ‘=‘– Ie., +=, -=, *=, /=, %=

• Examples:x += 2;

x += 2 * y;

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Library Functions

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Library Functions

• Library functions:– Commonly-used functions– Packaged together as a “library”– Gain access to them by:

• Including the library in your program• AND telling the compiler to link to the library

• Example: using the math library

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Common <math.h> Functions

• Note: all arguments/return-values are doubles

(absolute value)

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Random Numbers

• Generating truly random nums is hard!– Eg., gambling machine pattern discovered– Why?

• Most programs use “pseudo-random” nums– not perfectly random, close enough

• rand() function– in program (at top): #include <stdlib.h>– rand() returns an integer within 0..RAND_MAX

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Example using rand()

• Generate a random int between 0 and 1

• Generate a random int between 0 and 100

• Generate a random int between 1 and 10

• Generate a random even int bet. 2 and 10

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Mixing Types and Casting

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Mixing Types

• If multiple types are used in an expression– the wider (more accurate) type is “contagious”

• Example1:2 + 5.3 .

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Mixing Types: Example2

8 / 3 + 1.0 //

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Casting

• Casting lets you change one type into another– use casting to get the result type you want!

int x = (int) 5.7; //

• Precedence of cast: – higher than * /– lower than ++ --

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Cast Examples

int x = (int) 5.7 + 8.9;

int x = (int) (5.7 + 8.9);

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More Cast Examples

int x = (3 / 4) * 8; //