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Unit 3 Programming Calculations Using Numeric Data Introduction to C Programming

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Review of Unit 2 Unit 3: Review

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Review: Conversion Program #include int main(void) { double dist_in_miles, dist_in_kms; printf("Convert miles to kilometers\n"); printf("Please enter the distance in miles: "); scanf("%lf", &dist_in_miles); dist_in_kms = 1.609 * dist_in_miles; printf("The distance in kilometers is: "); printf("%f", dist_in_kms); return (0); }

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Performing Calculations Unit 3: Arithmetic Operators and Assignment Statements

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Assignment Statement Used to change a variable Stores a value, or computational result, in a variable Looks like equation, but is NOT o Left side of assignment must be a variable (called lvalue) o Right side of assignment is expression = ; Meaning: "Put value of into " o Previous contents of are lost o Data type of should match data type of

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Assignment Statement Examples days = 8; dist_in_kms = 1.609 * dist_in_miles; value = value * 2; result = value - 10; average = sum / 3;

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Expressions Could be a constant 52.6 Could be a variable numberOfTurns Could be a simple or complex calculation using operators setting + 1 ((tempF - 32.0) * (5.0/9.0))

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Arithmetic Operators Table 2.6 Remember: A number with a decimal point has the 'double' data type. A number without a decimal point has the 'int' data type.

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Mixed-type assignments int m, n; double p, x, y; m = 3; n = 2; p = 2.0; x = m / p; /* result is 1.5 */ y = m / n; /* result is 1.0! */ If both operands are int, the division is an int. The type of the target does not matter to the division.

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Assigning to an int vs. a double double x; int n; x = 9 * 0.5; n = 9 * 0.5; Assigning to an int variable truncates (the fraction part is discarded) 4.54 xn

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Casting an expression's type This calculation produces the "wrong" answer: int totalScores, numStudents; double average; totalScores = 569; numStudents = 6; average = totalScores / numStudents; o If the totalScores is 569, and numStudents is 6, the result in C is 94, but the desired answer is 94.83. o Why ? Because the division is done with two ints. By using a cast, we can promote the calculation to be a double: average = (double)totalScores / numStudents; Now, average is assigned 94.83

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Classification of Operators Unary OperatorsBinary Operators One operand a o Negation (-) o Positive (+) Examples: x = -y; y = -3.1; p = +x; Two operands a b o Add (+) o Subtract (-) o Multiply (*) o Divide (/) o Remainder (%) or 'modulo' Examples: x = t + 4; z = 5 * x; y = (2 - y) / z; i = g % 2;

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Rules of Precedence Which operation is done first? (3 + x) * y / (height * 1.1 - 17) Specifies order of operations in complex expressions o Parentheses Precedence Rules o Operator Precedence Rules o Associativity Rules

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Parentheses Precedence Rules What is inside parentheses is evaluated first. o Used to overrule the natural operator precedence order o Example: (2 + 10) * 3/* result is 36 */ Nested parentheses - innermost set is evaluated first. o Example: (2 + (10 - 1)) * 3/* result is 33 */

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Operator Precedence Rules Unary operations are performed first. Multiplication and Division operations are second. Addition and subtraction are last. Example: -3 + 7 * 2/* result is 11 */ The unary negation is first:(-3) + 7 * 2 The multiplication is next:(-3) + 14 The addition is last:11

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Associativity Rules Multiple multiplication / division are done left-to-right: 8/2*4/* result is 16, not 1 */ Multiple addition / subtraction are done left-to-right: 8-4+1/* result is 5, not 3 */

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Example from Electronics

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Creating a Named Constant To use a constant in a C program, create a named constant. o Created with #define, which defines a macro o Names are traditionally written in all caps. o The definition goes at the top of the file, with #include. #define PI 3.14159

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Example - Area of a Circle

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Example Program - Compute Area #include #define PI 3.14159 int main(void) { double radius, area; printf("Enter radius of a circle: "); scanf("%lf", &radius); area = PI * radius * radius; printf("Area is %f\n", area); return (0); }

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Use of const Keyword Another means of specifying a constant: o Standardized with ANSI C The const keyword specifies a read-only variable: o The variable cannot be changed by the program const double PI = 3.14159; No assignment statement is allowed: PI = 0;/* Compiler prevents this */

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Advanced Use of printf( ) Unit 3: More on the printf( ) Function

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Formatting Output of Type int Table 2.11 Displaying 234 and -234 Using Different Placeholders

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Formatting Output of Type double Table 2.13

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Formatting Currency Amounts Assume you have a dollar-and-cents amount to print: double coinsInDollars; What printf statement would you use to print a dollar sign, followed by a number with two decimal digits? The answer is: printf("$%.2f", coinsInDollars);

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C Standard Libraries Unit 3: Library Functions

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C Standard Libraries We have already seen the use of for I/O functions: o printf o scanf The library is a collection of prewritten calculations. Examples: double x, y; x = pow(10, y); /* Calculates 10 ^ y */ x = sqrt(y); /* Calculates square root */

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Table 3.1 pg 121 For more information on the math library, Google "math.h C library"

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The enum Data Type Unit 3: Enumerated Data Types

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The enum Data Type With typedef keyword, creates a new data type List of identifiers Compiler associates these with constants First in list is 0, next is 1, and so on typedef enum { SUN, MON, TUE, WED, THU, FRI, SAT } days_t; days_t today; today = SUN;/* 'today' is set to 0 */ printf("%d", today);/* prints '0', not "SUN" */

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Example: Color Bands enum Consider the Example below - what does this do? #include typedef enum { BLACK, BROWN, RED, ORANGE, YELLOW, GREEN, BLUE, VIOLET, GRAY, WHITE } colorbands_t; int main(void) { colorbands_t firstBand = ORANGE; colorbands_t secondBand = RED; colorbands_t thirdBand = BROWN; double res; res = (firstBand * 10 + secondBand) * pow(10, thirdBand); printf("Resistance is %.f\n", res); return (0); }

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Enum Data Type - Starting Value An enum data type typically starts the first enum at 0: typedef enum {ZERO, ONE} binary_t; However, C provides a way to start the first enum at a different value: typedef enum {A=1, B, C, D} alphabet_t; (A is 1, B is 2, C is 3, D is 4)

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Making Programs Appear Professional Unit 3: Coding Standards

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Coding Standards Purposes o Make code easier to read and understand o Make maintenance easier Corporate policies or guidelines Includes o Variable naming o Code formatting o Comments o Human factors

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Variable Naming Be consistent in naming styles o Camel Case: dayOfWeek o Underscores: day_of_week Pick meaningful names Avoid excessively long names Examples: double inputCurrent, outputVoltage; int partCount, loopCount; Don't use such obscure or confusing names as: double x, yy, my_football_team_rocks;

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Code Formatting A program that looks good is easier to read. Indent the body of a function Insert spaces and blank lines for readability Place only one statement on a line These techniques are demonstrated in class materials and text.

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Comments Use comments (not too few, not too many) Comment code that is not obvious Consider it a courtesy to yourself and those who come after For the class lab assignments: - Put the following information every time /* Your name */ /* ET2560 - Instructor's name */ /* Unit # Lab # and Task # */

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Human Factors Make programs user-friendly o Use spacing appropriately for separation as needed o Use newline characters in printf to create blank lines as needed Spell correctly, especially in program output Provide self-explanatory output text Design a simple, easy-to-understand interface Keep input and output neatly formatted

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Coding Standards Example #include #define PI 3.14159 /* Your name */ /* This program accepts the radius of a circle, calculates the area, and outputs the radius and the area. */ int main(void) { double radius; /* Stores radius entered by the user */ double area; /* Stores area after the calculation */ printf("Enter the radius of the circle: "); scanf("%lf", &radius); /* Calculate area as PI times r-squared */ area = PI * radius * radius; /* Output the area */ printf("The area of a circle with radius %f is %f\n", radius, area); return(0); }

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