ENG1410 C Programming: Topic #2 “C Programming: Variables ...

ENG1410C Programming: Topic #2

“C Programming: Variables & Identifiers

Part 1”S. Areibi

School of EngineeringUniversity of Guelph

Topics

Introduction to C C Tokens .. C Program Structure .. Comments .. Identifiers .. C defined Types …. Variables ..

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Textbook Resources

Chapter #3,

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C Tokens

C is a structured programming language. It isconsidered a high-level language because it allows theprogrammer to concentrate on the problem at handand not worry about the machine that the programwill be using. That is another reason why it is used bysoftware developers whose applications have to run onmany different hardware platforms.

C Language

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Keywordso These are reserved words of the C language. For example int,

float, if, else, for, while etc.

Identifierso An Identifier is a sequence of letters and digits, but must start with a

letter. Underscore ( _ ) is treated as a letter. Identifiers are case sensitive. Identifiers are used to name variables, functions etc.

o Valid: Root, _getchar, __sin, x1, x2, x3, x_1, Ifo Invalid: 324, short, price$, My Name

Constantso Constants like 13, ‘a’, 1.3e-5 etc.

Tokens in C

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String Literalso A sequence of characters enclosed in double quotes as “…”. For

example “13” is a string literal and not number 13. ‘a’ and “a” are different.

Operatorso Arithmetic operators like +, -, *, / ,% etc.o Logical operators like ||, &&, ! etc. and so on.

White Spaceso Spaces, new lines, tabs, comments ( A sequence of characters enclosed

in /* and */ ) etc. These are used to separate the adjacent identifiers,

kewords and constants.

Tokens in C

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C Structure

Structure of C Program

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Greeting Program

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Greeting Program

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Any thing between /* …. */ is a comment

The compiler will not pay any attention to it

Comments are useful to document your programs

Greeting Program

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Greeting ProgramOnce you compile your program and execute it, it will produce the following:

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Greeting ProgramWhenever a \n is encountered a new line is printed

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Comments

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Comments in C

C Example: Simple

Your First C Program

/* A simple program that prints something */

#include <stdio.h>

main (){

printf ("Hello, world!\n");}

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Output on the Screen Hello, world!

"The only way to learn a new programming language is by writing programs in it" [K&R]

C: Identifiers

One feature present in all computer languages isthe identifier.

Identifiers allow us to name data and other objectsin the program.

Each identified object in the computer is stored at aunique address.

Identifiers

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Rules for Identifiers

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An identifier must start with a letter or underscore: it may not have a space or a hyphen.

Note

C is a case-sensitive language.

Note

Valid vs. Invalid Names

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C: Types

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C Types

A type defines a set of values and a set of operations that can be applied on those values.

C Variable Typeso The most common types are: char, int, float, and double.o Strings are arrays of characters (we’ll cover arrays later).o Declare a variable before you use it:

int x;/* declares an integer called x. Its value is not assigned. */

float y, z = 3.14159; /* declares two floating point numbers -- z is set equal to pi */

z = 4;/* now z is equal to 4 */

myVal = 2; /* This would be an error, because myVal was not yet declared */

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C Types: Char

Characterschar a, b, c1, c2;a = '0'; b = '\037'; c1 = 'K'; c2 = c1 + 1;

• Assigns values: 48, 31, 75, 76• The sequences '0',...,'9', 'a',...,'z', 'A',...,'Z' contain characters numbered consecutively

Castingprintf ("%c %d\n", c1, (int) c1);

• Outputs: K 75

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Char: ASCII Characters

ASCII, abbreviated from American Standard Code for Information Interchange is a 7-bit code, meaning that 128 characters (27) are defined. The code consists of 33 non-printable and 95 printable characters and includes both letters, punctuation marks, numbers and control characters.

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C Types: Char#include <stdio.h>int main() {

char c;printf("Enter a character: ");scanf("%c", &c);

// %d displays the integer value of a character// %c displays the actual characterprintf("ASCII value of %c = %d", c, c);

return 0;}

Output

Enter a character: GASCII value of G = 71

In this program, the user is asked to enter a character. The character is stored in variable c.

When %d format string is used, 71 (the ASCII value of G) is displayed.

When %c format string is used, 'G' itself is displayed.

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C Types: Char (Example)Write a program that reads from the user a lower case letter, and prints its corresponding upper case letter.

#include <stdio.h>int main() {

char lowercase;char uppercase;

printf(“Please enter a lower case letter: ");scanf("%c", &lowercase); // Since the difference between lower case and upper case is 32 uppercase = lowercase -32;// display the upper case equivalent of the lower case letterprintf(“The upper case of %c is %c", lowercase, uppercase);return 0;

}Output:Please enter a lower case letter: t

The upper case of t is T

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C Types: Integers

sizeof (short) ≤ sizeof (int) ≤ sizeof (long) ≤ sizeof (long long)

Note

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C Types: int

In this program, an integer variable number is declared.

Then, the user is asked to enter an integer number. This number is stored in the number variable.

Finally, the value stored in number is displayed on the screen using printf().

#include <stdio.h>int main() {

int number;

printf("Enter an integer: "); // reads and stores inputscanf("%d", &number);// displays outputprintf("You entered: %d", number);

return 0;}

Output

Enter an integer: 25You entered: 25

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C Types: Float

sizeof (float) ≤ sizeof (double) ≤ sizeof (long double)

Note

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IEEE 754 Single PrecisionThe IEEE 754 standard specifies the single precision binary floating point as follows:

o Sign bit: 1 bito Exponent width: 8 bitso Significant precision: 24 bits

• The sign bit determines the sign of the number.• The exponent is an 8-bit unsigned integer from 0 to 255.

In baised form, an exponent value of 127 represents the actual zero. Exponents range from -126 to +127

• The true significand includes 23 fraction bits to the right of the binary point

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C Types: float/double

In this program, the user is asked to enter two numbers which are stored in variables a and b respectively.

Then, the product of a and b is evaluated and the result is stored in product.

Finally, product is displayed on the screen using printf().

#include <stdio.h>int main() {

double a, b, product;printf("Enter two numbers: ");scanf("%lf %lf", &a, &b);

// Calculating productproduct = a * b;// %.2lf displays number up to 2 decimal pointprintf("Product = %.2lf", product);

return 0;}

Output

Enter two numbers: 2.4 1.12Product = 2.69

StringsStrings are '\0'-terminated arrays of char :

char s[3] = "hi"; /* invisible '\0' */char t[3] = {'h', 'i', '\0'};

String operations#include <string.h>strlen ("there"); /* returns 5 */strcpy (s, t); /* copy t to s */strcmp (s, t) /* alphabetical comparison */

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C Types: Strings

Here, using a for loop, we have iterated over characters of the string from i = 0 to until '\0' (null character) is encountered. In each iteration, the value of i is increased by 1.

When the loop ends, the length of the string will be stored in the i variable.

Note: Here, the array s[] has 19 elements. The last element s[18] is the null character '\n'. But our loop does not count this character as it terminates upon encountering it.

#include <stdio.h>int main() {

char s[] = "Programming is fun";int i;

for (i = 0; s[i] != '\0'; ++i);

printf("Length of the string: %d", i);return 0;

}

Output

Length of the string: 18

C: Variables

Variables are named memory locations that have atype, such as integer or character, which is inheritedfrom their type.

The type determines the values that a variable maycontain and the operations that may be used with itsvalues.

Variables

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Variables in Programming Represent storage units in a program Used to store/retrieve data over life of program Type of variable determines what can be placed in

the storage unit Assignment – process of placing a particular value in

a variable Variables must be declared before they are assigned The value of a variable can change; A constant

always has the same value

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Naming Variables When a variable is declared it is given a name Good programming practices

Choose a name that reflects the role of the variable in a program, e.g.

• Good: customer_name, ss_number;• Bad : cn, ss;

Don’t be afraid to have long names if it aids in readability Restrictions

Name must begin with a letter; otherwise, can contain digits or any other characters. C is CASE SENSITIVE! Use 31 or fewer characters to aid in portability

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Declaring Variables All variables must always be declared before the first

executable instruction in a C program Variable declarations are always:

var_type var_name;o int age;o float annual_salary;o double weight, height; /* multiple vars ok */

In most cases, variables have no meaningful value at this stage. Memory is set aside for them, but they are not meaningful until assigned.

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Variable Declaration All variables must be declared in a C program before

the first executable statement! Examples:

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void main(){

int a, b, c;float d;/* Do something here */

}

Variables: Declaration

Rules:• declarations must precede executable statements

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Variables: Declaration

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Variables: Declaration

Example:float x;double d = 5;int *p, i, a[100];char s[21];

Syntax:type variable_name, ... [= value];

Rules:• declarations must precede executable statements• int type may be modified by: long, short, unsigned

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Variable Assignment After variables are declared, they must (should) be

given values. This is called assignment and it is done with the ‘=‘

operator. Examples:

float a, b; int c; b = 2.12; c = 200;

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Variables: Initialization

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When a variable is defined, it is not initialized. We must initialize any variable requiring prescribed data when the function starts.

Note

Changing Variable Values

Example:int x, y, z;x = 2;x = x + 1;

Getting Fancyy = z = 4 + 5;x += 1;++x;x++;y = x--;

Note:• assignment statements return value, which may or may not be ignored; same goes for increment statements

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Variables: Example 1

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#include <stdio.h>

// program prints a number of type intint main() {

/* Declaring a variable called “number” of type integer */int number = 4;

printf (“Number is %d”, number);return 0;

}

Output on the Screen: Number is 4

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Variables: Example 2

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#include <stdio.h>// program reads and prints the same thingint main() {

/* Declaring a variable “number” of type integer */int number ;

printf (“ Enter a Number: “); scanf (“%d”, &number);printf (“Number is %d\n”, number);return 0;

}

Output on the Screen : (1) Enter a number: 4(2) Number is 4

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Variables: Example 3

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#include <stdio.h>#include <stdbool.h>int main (void){

int integerVar = 100;float floatVar = 331.79;double doubleVar = 8.44e+11;char charVar = 'W';bool boolVar = 0;

printf("integerVar (using %% i)= %i\n", integerVar);printf("integerVar (using %% d)= %d\n", integerVar);printf("floatVar (using %% f)= %f\n", floatVar);printf("doubleVar (using %% e) = %e\n", doubleVar);printf("doubleVar (using %% g)= %g\n", doubleVar);printf("charVar (using %% c) = %c\n",charVar);printf("boolVar (using %%i) = %i\n",boolVar);

return 0;}

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After executing this program:

integerVar (using %i) = 100integerVar(using %d) = 100floatVar (using %f) = 331.79doubleVar (using %e) = 8.44+011doubleVar (using %g) = 8.44+011charVar (using %c) = WboolVar = 0

Write a program that asks a user to enter the numberof days travelled.

The program would then display theo Full weeks traveledo Remaining days traveled

For example:o If the user entered 19o The program will displayo Full weeks traveled 2o Remaining days traveled 4

A Simple Program

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A Simple Program

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#include <stdio.h>/* program reads number of days travelled and prints fullWeeks, remainDays */int main() {

/* Declaring the variables */int daysTraveled;int fullWeeks, remainDays;

/* Prompt the user to enter the total number of days travelled */printf (“ Enter the total number of days travelled: “); scanf (“%d”, &daysTraveled);/* Calculate the # of weeks and remaining days of total daysTraveled */fullWeeks = daysTraveled/ 7;remainingDays = daysTraveled % 7;

printf (“%d days are %d weeks and %d days\n”, daysTraveled, fullWeeks, remainDays);return 0;

}

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Enter the total number of days traveled: 19

19 days are 2 weeks and 4 days

Size of Variables

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#include <stdio.h> int main() {

short a;long b;long long c;long double d;

printf("size of short = %d bytes\n", sizeof(a));printf("size of long = %d bytes\n", sizeof(b));printf("size of long long = %d bytes\n", sizeof(c));printf("size of long double= %d bytes\n", sizeof(d));return 0;

}

• You can always check the size of a variable using the sizeof () operator.

Summary

Summary C is a structured high level programming language that is used

extensively by software developers. One feature present in all computer languages is the identifier

that allow us to name data and other objects in the program. A type in the C programming language defines a set of values

and a set of operations that can be applied on those values. The most common types in the C programming language are:

char, int, float, and double. Variables are named memory locations that have a type, such

as integer or character, which is inherited from their type. The type determines the values that a variable may contain and

the operations that may be used with its values. Constants are data values that cannot be changed during the

execution of a program. Like variables, constants have a type.

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Resources

C Variables/Types: Resourceso YouTube:

https://www.youtube.com/watch?v=gsQX0VKPBws https://www.youtube.com/watch?v=k1ur8rX-DQQ https://www.youtube.com/watch?v=j1u3V6pzwEI

o Documents: https://www.unf.edu/~wkloster/2220/ppts/cprogramming_tutorial.pdf

o Examples: https://beginnersbook.com/2015/02/simple-c-programs/ https://www.studytonight.com/c/programs/ https://www.programiz.com/c-programming/examples

o Test Yourself: https://www.javatpoint.com/c-quiz https://www.tutorialspoint.com/cprogramming/cprogramming_online_quiz.htm https://data-flair.training/blogs/online-c-programming-test/

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