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# day4 - Basics of Algorithms Basic Tools for Building...

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Basic Tools for Building Algorithms Atomic Data - Numbers: integers, real (floating point) - Characters: alphabetic and symbols - Booleans: true/false - Pointers: reference memory addresses (locations) Operators - Assignment: number1 = number2 - Arithmetic: +, -, *, /, ^ - Input/Output: scanf, printf (in C) - Relational: <, >, ==, etc. - Boolean: and, or, not Creating Simple Variables A variable can be thought of as a named box, or cell, in which one or more data values are stored and may be read or written by the algorithm. An atomic variable is a variable that can hold only 1 individual piece of data, such as a number or a character. The act of creating a variable is called declaring the variable . For every variable that is declared it must be explicitly typed. In other words, each variable has an associated data type . An identifier is simply the algorithmic terminology for a name that we “make-up” to “identify” the variable. Every variable must be given a unique identifier so that there will be no ambiguity as to which piece of data we are referencing. Examples int age; /* declares a variable named age whose type is integer */ int test_score; float average; /*declares a variable named average of type float */ Algorithms - 12 Basics of Algorithms

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Rules for Variable Identifiers in C A sequence of letters, digits, and the special character _ (underscore). A letter or the underscore character must be the first character of an identifier. The C language is case-sensitive. This means that first and First are two different identifiers. Atomic Data Types in C Numbers - int : 4 bytes - short : 2 bytes - long : 4 bytes - unsigned : 4 bytes - float : 4 bytes - double : 8 bytes - long double : 8 bytes The range of values that can be stored in each type depends upon the particular computer hardware on which the program will be executed. Characters - char : 1 byte Examples char your_grade; char first, middle, last; int age, year; A variable can be assigned an initial value at the time it is declared. int height = 75; char grade = ‘A’; Algorithms - 13
Pointers Pointers are used to access memory and manipulate memory addresses. int alpha; /* alpha is an integer variable */ int *ptr; / * ptr is a pointer to an integer */ alpha = 7; /* value of 7 is assigned to alpha */ ptr = α /* ptr is assigned to reference the location named alpha */ ptr alpha printf(“%d\n”, *ptr); /* prints the contents of the address referenced by ptr */ We’ll cover pointers in much more detail later, for now just be aware that they are an atomic data type in C. Arithmetic Operators in C The four basic arithmetic operators are provided in C along with the modulus operator. Addition:

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day4 - Basics of Algorithms Basic Tools for Building...

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