Your First 3 C Programs Made Easy

Variables allow us to specify values in our program that we can reference throughout our code. We can think of variables as buckets or placeholders for our code.

• Buckets have a limited space -each variable we declare in C will have a fixed size.
• Buckets have a unique shape -variables are designated to store integers, decimals, characters or pointers.
• We do not have an infinite supply of buckets -the more variables we introduce into our program, the more RAM it will take to function. This is not much of a concern with advances in computing, but it is worth noting.

Declaring Variables and Instantiation

Using the same analogy, we can allocate space in our program to fit buckets that we will need in order to do our computation. This step is called declaration. We can think of this step like we are taking publicly used buckets on the beach for our sand castle project. This way, no one else comes and takes our buckets until we are done using them. When our program closes, we will give back this buckets back so that others may use them. Tying it all together, we can request more space from the system for variables and give this space back when we are finished with the program.

There are two components to declaring a variable: the variable type and name. The variable type defines what kind of variable we would like. There are a variety of types we can declare -each with a fixed allotted space. The variable name is what we will use to reference this space. In doing so, C can support multiple variables of the same type, however, each must have a unique name like so:

int a;

double b;
double c;
float f;

char d;
char *e;

We have multiple variables declared. a is an integer which can store integers. b and c are both double variables. Doubles and floats can be used to store floating point numbers (or numbers with decimal points). Doubles get their name because they are double the size of floats. Variable d is a character variable that stores one character. e is a fixed string, meaning it can store one string (multiple characters put together), however the only way to change this value is to provide a new string.

The C language supports a couple of funky variable naming conventions, but in general we will use the following guidelines in this course for naming variables:

• Variables should start with a lowercase letter (the * in some variables are included in the type and do not count towards the name.)
• Variables describe what their purpose our in a short and sweet manner
• Variables are snaked_cased_like_this or camelCasedLikeThis (pick one and stick with it in your program)
• Variables can have numbers after the first letter like so: i1, i2, i3.

Instantiation

We have our buckets we can work with, however, they do not have much meaning to us at the moment. Since our buckets are publicly used, there is no telling what the previous user did with them and if they left anything there. Similarly, the space we get from our system will have random values. It is important to instantiate your variables, or give them a starting value. We can do this in the following manner:

int my_favorite_number;
my_favorite_number = 0;

We can change the value of our variable later in the code like so:

my_favorite_number = 4;

Since we’ve already declared that my_favorite_number is an integer variable, we do not need to put int in front of it afterwards; the program just needs the name of our variables after declaration.

If we know the value we want our variable to be at the time of declaration, we can do a declaration/instantiation like so:

int my_favorite_number = 4;

This applies to all variable types! Copy the following code into your terminal and give it a try:

#include <stdio.h>

int main(void)
{
   int a = 1;
   double pi = 3.14;
   char *string = "Hello World!";
   char c = 'C';

   // Printing our variables
   printf("a = %d\n", a);
   printf("pi = %f\n", pi);
   printf("%s\n", string);
   printf("My char is %c\n", c);
   return 0;
}

You can always change the value stored in your variable after you instantiate it. This is called an assignment or reassignment operation.

Print Formatting

You may have noticed a couple of weird characters in the print statements. Those are format specifiers. This tells our compiler that we are going to print out the values stored in our variable. To do this in C, we specify what type of information we will be printing. After our print statement, we include our variable that we would like to print. The type specified should match the variable you enter at the end of the string.

• %d: integers
• %f: floating point numbers
• %c: characters
• %s: strings
• %p: pointers (more on this later)

You can have multiple variables printed in the same print statement. They can also have different data types too -just be sure you don’t mix them up.

#include <stdio.h>

int main(void)
{
   int a = 1;
   int b = 2;
   double c = 3.0;

   printf("%d %d %f\n", a, b, c);
}