CSC 107 -Programming for Science

Lecture 5:

Actual Programming

Today’s Goal

At the end of today’s lecture, you should be able to write a reasonable C programThis includes input & output!We will have a real lab this week!

Variables

Variables name memory location for program to store dataVariable’s initial value is unknownAssignments update data stored at memory

locationVariable’s value used whenever program uses

variable

Data Types

Each variable also has data type Specifies how program treats variable’s value

C defines 6 numeric data types Integer types: short, int, long Decimal types: float, double, long double Does NOT specify ranges for each type

char data type holds a character C will only allow certain assignments

Assign an integer to a decimal variable --- easy Assign decimal to integer variable --- not easy

More Data Types

Each numeric data type is actually 2 typessigned (default) and unsignedint i, j, k;unsigned double l, m, n;

Unsigned data must be non-negativeUpper range of variable is doubledUseful for some data: degreesKelvin,

timeObservation, weight, homeworkScore C compiler emits warning when mixing

signed & unsigned data

Printing Out Results

C defines function to print information outFunction is called printf Information is printed out in window where

program is runArguments to printf determine what is

printed printf’s arguments can be very esoteric

Do not memorize; this is why manuals exist

printf

printf(“Hi, Mom\n”); First argument must be in quotes Except for a few magic commands, it

prints out what you specify\n print out newline\t print out tab\\ print out “\” character\b sound error bell

Even Better Magic

Must tell printf how to format variables

C will not complain for wrong specifier, but results are bad

Variable Type Specifierint %i, %dshort %hi, %hdlong int %li, %ldunsigned int %uunsigned short %huunsigned long %lufloat %f, %e, %E, %g, %Gdouble %lf, %le, %lE, %lg, %lGlong double %Lf, %Le, %LE, %Lg, %LGchar %c

Printing Out Data

Identifier placed in first argument Identifier replaced with value of variable, symbolic

constant, or literal

Values supplied in next arguments Must be included in order identifiers appear

caveat emptor when using function Compiler does NOT check identifiers or argument Too many can cause later problems Too few arguments results in odd printouts

printf Examples

double d;int i;unsigned int u;printf(“This is a boring example.\n”);

printf(“Prints a double -- %f\n”, d);

printf(“Prints 2 digits beyond decimal -- %.2f\n”, d);

printf(“Prints an int -- %d\n”, i);

printf(“Prints an unsigned int %u\n”, u);

printf(“Prints i’s (%d) & u’s (%u) value”, i, u);

printf(“i + u = %u\t i + d = %d\n”, i+u, i+d);

printf(“Printing a percent sign is 100%% hard”);

scanf

C defines scanf to get user’s inputVery similar in usage to printfSets variables equal to values input on

keyboard scanf waits until it has input

Wait could be years if nothing is inputLines cannot be read until enter is pressed

Arguments to scanf

First argument must be in quotes Must state type of data to be read

Uses same identifiers as printf Afterward specify variables to assign

Data types should match (otherwise program results will be odd)

Need to list “&” before each variable name

scanf Examples

double d;int i;unsigned int u;scanf(“%u”, &u);

scanf(“%f %d\n”, &d, &i);

scan(“%f\n%d”, &d, &i);

scanf(“%f%%\n”, &d); Ampersand (&) before each variable name is vital

Needed to assign variable a new value

Your Turn

Get into groups and complete daily activity

For Next Lecture

Read through Section 2.6 of bookDo not need to understand all the detailsBut important knowing what is not understood

Start homework assignment for week 3Covers material from this week’s lectures