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

Learning Objectives

How to write a simple C program

How to compile it

How to execute it

We will also explain some common errors and their solution.

System Requirements

Ubuntu operating system version 11.10

and GCC Compiler version 4.6.1 on Ubuntu.

Prerequisites

You should be familiar with Ubuntu Operating System.

And an editor.

Some editors are vim and gedit

I will use gedit in this tutorial.

For relevant tutorials please visit our website as shown:

http://spoken-tutorial.org

Open the terminal using Ctrl + Alt + T or alternately,

Click on Applications-> Accessories -> Terminal

At the command prompt type: gedit firstprog.c

Type:

//My first C program

Open the terminal Window by pressing Ctrl, Alt and T keys Simultaneously on your keyboard.

Now lets open the text editor, So at the prompt type:

"gedit" space "talk" dot "c" space &

We used the ampersand(&) to free up the prompt

Please note that all the C files will have extension dot "c"

Now Press Enter.

The text editor has opened.

Let us start to write a program.

Type double slash “//” space

“My first C program”.

Comments are used to understand the flow of program.

It is useful for documentation.

It gives us information about the program.

The double slash is called as single line comment.

#include <stdio.h>

Type "hash (#) include (space) opening bracket, closing bracket.

It is always a good practice to complete the brackets first, and then start writing inside it.

Now, Inside the bracket, type:

"stdio" dot "h"

stdio.h is a header file

A program must contain this header file when it uses standard input/output functions

Now press Enter

int main()

main() is a special function.

It denotes that the execution of the program begins from this line.

The opening bracket and closing bracket is called as paranthesis.

Paranthesis followed by main() is to tell the user that main is a function.

Here the int main() function takes no arguments. It returns a value of type integer.

We will learn about data types in another tutorial.

Now let us switch to the slides to know more about the main() function.

Let us go tot he next slide.

There should NOT be more than one main function .

Otherwise, the compiler cannot locate the beginning of the program.

The empty pair of parentheses indicate that main has no arguments.

The concept of arguments will be discussed in detail in the upcoming tutorials.

int main()

{

Press Enter

type: { (opening curly bracket)

The opening curly brace marks the beginning of the function main.

int main()

{

}

The Closing bracket indicates the end of the function main.

press enter twice, move the cursor one line up

It also helps to locate errors faster

So let us give three space here.

int main()

{

printf("Talk To a Teacher \n");

printf and opening bracket and closing bracket ()

printf() is a standard C function to print the output on the terminal.

Here inside the brackets, within double quotes,

Anything within the double quotes in the printf statement will be printed on the terminal.

Type:

Talk To a Teacher backward slash (\) and "n"

\n (Backward Slash n) signifies newline,

As a result after the execution of the printf function the cursor moves to the new line.

Every C statement must end with a semicolon(;)

Hence Type it at the end of this line.

Semicolon(;) acts as a statement terminator.

int main()

{

printf("Talk To a Teacher \n");

return 0;

}

Give three space here.

And type 'return (space)0' and a semicolon ';'

This statement returns the integer zero.

An integer has to be returned for this function

Because the function type is int.

The return statement marks the end of the executable statements.

We will learn more about the returned values in another tutorial.

int main()

{

printf("Talk To a Teacher \n");

return 0;

}

Type:

gcc talk.c -o myoutput

Highlight

gcc

talk.c

-o myoutput

It is a good habit to save files frequently.

This will protect you from sudden power failures.

It will also be useful in case the applications were to crash.

Let us now compile the program

Come back to our terminal

Type: "gcc" space “talk.c” space hyphen o space “myoutput"

gcc is the compiler

talk.c is the filename

-o myoutput says that the executable should go to the file myoutput.

And press Enter

We see that the program is compiled.

ls -lrt

./myoutput

type ./myoutput (dot slash "myoutput")

press Enter

Here the output is displayed: "Talk To a Teacher".

Thus after the return statement nothing will be executed.

Let us try it out.

Come back to our program.

Give space here.

printf and opening bracket and closing bracket ()

inside the brackets, within double quotes,

type: “Welcome” backslash n

At the end type a semicolon ;

Let us compile and execute.

Come back to our terminal.

You can recall the previously entered command by using up arrow key.

That is what I did now.

We see that the second statement Welcome is not executed.

Let us write the Welcome statement above the return statement.

Let us compile and execute

Type:

<stdioh>

Come back to our program.

Now suppose I will miss the dot '.' in

<stdio.h>

Click on Save

Let us compile and execute.

we see that there is an fatal error at line no.2 in our talk.c file.

The compiler cannot find a header file with the name “stdioh”

Hence it is giving an error "No such file or directory" and the compilation is terminated.

Come back to our program.

Reinsert the “.”

Let us compile and execute.

Yes it is working.

Type:

printf("Hello World \n")

Let us switch back to the program.

Now, suppose here I will miss the semicolon at the end of the line.

Click on Save

Let us compile and execute.

we see an error at line no.6 in our talk.c file.

That expected semicolon before printf.

Come back to our program.

As I said before, semicolon acts as a statement terminator.

So it will search for it at the end of the line 5 and at the begning of the line 6.

This is line 6.

This is the last place where you can put the semicolon.

Recall that compiler also gave the error message on line 6.

Click on Save.

Yes it is working.

Let us type the semicolon here at the end of this line.

As it is the conventional practice to type the semicolon at the end of the line.

Let us compile and execute.

Yes it is working.

Now let us move back to our slides.

Assignment

Write a program to print "Welcome to the World of C"

See what happens if \n is not included in the printf statement.

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