Learning C

We will be doing this lab inconjuction with the C lecture. Key concepts will be explained and you will put into practice.

So let's make our first program.

1. First C Program

1. Create a new directory and call it ELEE1119/Learning_C we can do this using the following commands in terminal.

   Terminal

   $  mkdir -p ELEE1119/Learning_C
   

   Warning

   • the $ symbol used in the above indicates that this is a command that should be entered into the terminal.
   • these are shell commands written in c.

2. Now you are to navigate to this directory using the following command and create your first file:

   Terminal

   $  cd ELEE1119/Learning_C
   $  touch helloworld.c
   

   Note

   Each line should be entered in seperately

3. If we use the command ls we can list the content of the directory and should see at a file named 'helloworld.c'

   Terminal

   $ ls
   

   Output

   helloworld.c
   

4. Now we are going to open up and edit the content of the file and write it out:

   Terminal

   $ vim helloworld.c
   

5. Enter the following:

   Code

   #include <stdio.h> // we need this library to get access to the input and out put methods for printing to terminal
   
   int main()
   {
       printf("Hello World\n"); // lets say hello, where it all began...
       
       printf("Goodbye World\n"); // this seems fitting as the program will close after this.
       
       return 0; // returns 0 to the int of main() and terminate the program
   }
   

   Tip

   • To use i to enter INSERT mode

   • Escape key to current mode into COMMAND mode

   • :wq write and quit

   Explanation

   Some explanation about the above code:

   • All code gets executed inside of main(),

   • For the program to terminate the main() has to have a returnable value, int,

   • The keyword at the end of the main() is return, this is will return the value preceeding it,

   • A 0 execute means no errors.

   • Similar to C# to use libraries c programs import with the #include keyword instead of using.

   • The included library is the standard input out header, stdio.h.

   • By including this header file we have access to the printf() function that enables us to return information to the terminal in string format.

6. Now we are going to compile the code so that we have an executable file that can be run from the terminal:

   Terminal

   $ gcc helloworld -o helloworld.exe
   

   Info

   • gcc is another shell command that is built in c, it's purpose is to compile .c files into executables using the the gcc.

   • Using the option -o we specifiy the output path/to/file

   • For more info -> gcc

7. Now let's see the fruits of our labour, the file can be executed as follows:

   Output

   $ ./helloworld.exe
   Hello World
   Goodbye World
   

   Success

   Congratulations, you used the programming language of the gods!

2. Input/Output functions

1. Create a new file vim inputoutput.c and reproduce the code below:

   Code

   #include <stdio.h>    
   int main()
   { 
       // Displays the string inside quotations
       printf("C Programming");
       return 0;
   }
   

   Tip

   Remeber to use the vim shortcuts from before to edit, write and quit.

2. Compile and run:

   Terminal

   $ gcc inputoutput.c -o inputoutput.anything
   $ ./inputoutput.anything
   C Programming
   

2.2 Data Type: Printing Integer

3. Now we are going to modifiy the script again $ vim inputoutput.c to look like below:

   Code

   #include <stdio.h>
   int main()
   {
       int testInteger = 5;
       printf("Number = %d", testInteger);
       return 0;
   }
   

   Explanation

   We use %d format specifier to print int types. Here, the %d inside the quotations will be replaced by the value of testInteger.

   Tip

   Remeber to use the vim shortcuts from before to edit, write and quit.

4. Run the script again...

   Terminal

   $ ./inputoutput.anything
   

   What happened?

5. Well we need to recompile the code.

   Output

   $ gcc inputoutput.c -o inputoutput.anything
   $ ./inputoutput.anything
   Number = 5
   
   

2.3 Data Types: Printing Float and Double

6. Open and modify the same file again to look like below:

   Code

   #include <stdio.h>
   int main()
   {
       float number1 = 13.5;
       double number2 = 12.4;
   
       printf("number1 = %f\n", number1);
       printf("number2 = %lf", number2);
       return 0;
   }
   

   Explanation

   To print float, we use %f format specifier. Similarly, we use %lf to print double values.

7. Compile the code again using format gcc <filesource> -o <fileoutput>...

8. Run it ./<fileoutput>:

   Output

   $ ./inputoutput.anything 
   number1 = 13.500000
   number2 = 12.400000
   

2.4 Data Types: Printing Characters

9. Open and modify the same file again to look like below:

   Code

   #include <stdio.h>
   int main()
   {
       char chr = 'a';    
       printf("character = %c", chr);  
       return 0;
   } 
   

   Explanation

   To print char, we use %c format specifier.

10. Remember to compile and then run:

    Output

    $ ./inputoutput.anything 
    character = a
    

2.5 User Input in C

11. Again we will modify the program to look like the code below:

    Code

    #include <stdio.h>
    int main()
    {
        int testInteger;
        printf("Enter an integer: ");
        scanf("%d", &testInteger);  
        printf("Number = %d",testInteger);
        return 0;
    }
    

    Explanation

    Here, we have used %d format specifier inside the scanf() function to take int input from the user. When the user enters an integer, it is stored in the testInteger variable.

    Notice, that we have used &testInteger inside scanf(). It is because &testInteger gets the address of testInteger, and the value entered by the user is stored in that address. We will cover addressing and pointers at a later date.

12. Compile and run:

    Output

    $ ./inputoutput.anything
    Enter an integer: 4
    Number = 4
    

3. Format Specifiers

Here is a table of possible format specifiers for input and output:

4. Data Types

1. Create a new file with vim like this:

   Terminal

   $ vim dataTypeSize.c
   

2. We are going to write a program that returns the size of each data type availabe in c.

   Code

   #include<stdio.h>
   int main(){
   
       printf("Data_Types\t\tStorage_Size \n");
       printf("char\t\t\t%d byte(s) \n", sizeof(char));
       printf("int\t\t\t%d byte(s) \n", sizeof(int));
       printf("double\t\t\t%d byte(s) \n", sizeof(double));
       printf("float\t\t\t%d byte(s) \n", sizeof(float));
       printf("unsigned char\t\t%ld byte(s) \n", sizeof(unsigned char));
       printf("long\t\t\t%d byte(s) \n", sizeof(long));
       printf("unsigned long\t\t%ld byte(s) \n", sizeof(unsigned long));
       printf("long double\t\t%ld byte(s) \n", sizeof(long double));
   
       return 0;
   }
   
   

   Terminal

   gcc dataTypeSize.c -o dataTypeSize
   

3. Now enter the following to see the data types and there available sizes in bytes:

   Output

   $ ./dataTypeSize
   
   Data_Types              Storage_Size 
   char                    1 byte(s) 
   int                     4 byte(s) 
   double                  8 byte(s) 
   float                   4 byte(s) 
   unsigned char           1 byte(s) 
   long                    8 byte(s) 
   unsigned long           8 byte(s) 
   long double             16 byte(s)