Difference between revisions of "C-and-C++/C2/Tokens/English"

To define and use tokens.

We will do this with the help of an example.

We will also see some common errors and their solutions.

Ubuntu Operating system version 11.10.

gcc and g++ Compiler version 4.6.1

Token is a generic word for Data types, Variables, Constants and Identifiers.

I have already typed the code on the editor

Let me open it

int main()

This is our main function.

int a = 2;

The compiler knows the meaning of keywords.

int a

int a = 2;

This is called as initialization.

double const b = 4

We have initialized b, by assigning a value of 4 to it.

double const b = 4;

Keywords cannot be used as variable names

There are 32 keywords available in C

To name some, auto, break, case, char, enum extern, etc.

They do not change during the execution of a program.

There are two types of constants.

Numeric constants. and

Character constants.

float c

float c = 1.5;

Data type is a finite set of values along with a set of rules.

char d = 'A';

Char and single quotes suggest that we are dealing with a character

As a result, d is a character variable

storing the value 'A'

a and c

a, c and d are variables.

Now come back to our slides.

We will know more about datatypes and variables.

It is declared as int

If we want to print an integer, we will use %d as the format specifier

Similarly, we will use float and %f for floating point numbers

For character data type, we will use char and %c

And for double data type, we will use double and %lf as the format specifier.

Integer value has a range of this.

Floating point has a range of this.

Character has a range of this.

And Double has a range of this.

The values stored in the variable must not be greater or less than this range.

Now we will move on to variables.

It may be used to store a data value .

The values can change when a program runs.

Before using a variable it must be declared.

We should try to give meaningful names to variables

example john, marks, sum etc.

printf("The Value of a is %d\n", a);

Let us know about identifiers.

An identifier consists of letters and digits

Both uppercase and lowercase letters are permitted

First character must be an alphabet or underscore.

Here we print them.

Now click on Save

Please open the terminal by pressing Ctrl, Alt and T keys simultaneously on your keyboard.

gcc tokens.c -o tok

gcc space tokens.c space -o space tok

press Enter

./var

./tok

Output

We can see that here we have six values after the decimal point.

And here we have two values.

Come back to our program.

printf("The Value of c is %.2f", c);

It denotes that we can print only two values after the decimal point.

%.2f with %.3f

Come back to the terminal

execute as before

1.500

Come back to our program.

<iostream>

<iostream>

using namespace std;

And click on Save.

cout<<

Since we use cout<< function to print a line in C++

printf(

cout <<

Type here printf opening bracket “(”

And here in this column type,

cout and two opening angle brackets “<<”.

Let us delete them.

Type two opening angle brackets.

delete (

Type << “\n”

Now delete the closing brackets.

Type two opening brackets again.

And within the double quotes type \n

Now Click on Save

Come back to the terminal.

gcc tokens.c -o tok1

Type

./tok1

To compile type:

gcc space tokens.c space -o space tok1

Here we have tok1

Because we don't want to overwrite the output parameter tok for the file tokens.c

Now press Enter

Type

./tok1

press Enter

Output

Type

%d

Come back to our program.

Suppose here I will reassign a new value to b as 8.

Let us see what happens.

Let me clear the prompt.

Now compile as before.

error

Assignment of read only variable b.

Come back to our program

This is because b is a constant.

Constants are fixed values.

They do not change during the execution of program.

Hence it is giving an error.

Delete this.

Click on Save

Let us execute again

Come back to our terminal

Execute as before.

Yes it is working.

Switch back to our program.

Click on Save

let us execute.

Compile as before.

A was not declared in the scope.

Come back to our program.

This is because anything within the single quotes is considered as a character value.

And here we have declared d as a character variable.

Type single quotes at line no.9 here.

Come back to our terminal

Now Compile as before

Execute as before.

Yes it is working.

Now switch back to our slides.

In this tutorial we learnt,

Data types

eg. int, double, float etc.

Variables

eg. int a=2;

Identifiers

eg. printf()

Constatnt

eg. double const b=4;

Assignment

Write a C program to calculate the simple interest.

Hint: Simple Interest = principal * rate * time / 100

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