CCPROG1_variables_operators

#public/classnotes

original file

Tokens in C

Introduction to the Syntax of C

Tokens include...

Geeks4Geeks: Tokens in C

Constants

String Literals

Identifiers

Data Type Prefix Valid Example
int n int nAge;
long l (lowercase L) long lLong;
float f float fTotal;
double d double dAmount;
char c char cJoke 
// --- IDENTIFIERS ---
my_variable // wrong: this is my var
input1 // wrong: tel#, 1stvariable, 7eleven, 200people
_MAX // wrong: money$
x //wrong input-number
for_loop_var // wrong: for
signed10 // wrong: signed
ans
ANS
aNs
Ans // these are all different

// --- VARIABLES AND HUNGARIAN NOTATION---
int nMyVariable, x, nMaxVal;
long var1, var2, var3;
float var4, varFive, varfive, fValue, fAverage;
double doubledouble, doubledoubledouble, DOUBLE, cFirstInit, cLast, ch1;

A series of Variables

A series of variables of the same type can be declared at the same time. Given that they are separated by commas and each list ends with a semi-colon. ; We did this in the example above.

Define Constants

// --- DEFINE CONSTANTS ---
// These are usually at the start of the file.
#define SCHOOL "De la Salle University"
#define PI 3.14
#define MAX_STRING_LEN 50
#define LETTER_A 'a'
#define ANSI_RED "\e[0;31m"
#define ANSI_OFF "\e[0m"

Operators

Operator Function
* multiplication
/ division
% modulo
+ addition
- subtraction
More on Operators

Attempting to perform arithmetic operations on variables with different datatypes will give you a result of another type. Whatever is the "larger" data type that can hold both values becomes the "overall" or resulting datatype.

Operator Description Precedence Associativity
() Parenthesis 1 - Highest Left-to-Right
unary +/- Positive or negative sign 2 Right-to-Left
*
/
%		 Multiplication
Division
Remainder/Modulo		 3 Left-to-Right
+
-		 Addition
Subtraction		 4 - Lowest Left-to-Right
Sample Math Equations Conversion
1.b2−4ac (= -23)2.a+bc−d (= -5)3.11+a2 (= 1/5 or 0.2)4.a⋅−(b−c) (= 2)

You can try running this code in VsCode (If you have C installed), DevC++, or in an online C compiler like Programiz! (See installing a c compiler on windows for a guide.)

#include <stdio.h>
int main() {
	int a, b = 3, c = 4, d = 5;
	a = 2; // note I didn't have to put "int" again
	int nFirstEquation = b*b - 4*a*c;
	int nSecondEquation = (a+b)/(c-d);
	float fThirdEquation = 1.0 / (1 + a * a);
	int nFourthEquation = a * -(b-c);

	printf("%d\n", nFirstEquation);
	printf("%d\n", nSecondEquation);
	printf("%f\n", fThirdEquation);
	printf("%d\n", nFourthEquation);
	return 0;
}
/* console output:
* -23 
* -5
* 0.200000
* 2
*/
Assignment Operator

This lets us store a value or a computational result in a variable. In mathematics, we use = as "equals" to signify the left-hand side and right-hand side are equal. In programming languages like C, it's the assignment operator.

Declaration vs Assignment vs Initialization

Declaration is when you create a variable by doing <datatype> <variable name>; without assigning it a specific value.

Assignment is simply giving the existing variable a value or expression. The syntax is <variable> = <expression>;.

Initialization is when you declare and assign a value to it like so: <datatype> <variable name> = <value>;

The code above declared and initialized multiple variables. So in the example, we declared a variable a. In the next line, we assigned it with a value of 2. We initialized b, c, d, and nFirstEquation up to nFourthEquation with values and expressions. You can assign defined constants to variables as well. For example:

#include <stdio.h>
#define PI 3.1415926535

int main() {
	float fMyPi = PI; // assign it to the constant we defined
	printf("%f", fMyPi); // output as is would be 3.141593
	return 0;
}

Note: It rounds up the 6th decimal point up. If we specified it to be printf("%.10f, fMyPi);, it would print the entire thing.

Shortcuts

There are some shortcuts in C. It just makes everything cleaner. For example:

#include <stdio.h>
int main() {
	int nMyInt = 2;
	printf("nMyInt as is: %d", nMyInt);
	nMyInt = nMyInt + 1;
	printf("nMyInt when incremented the long way: %d", nMyInt);
	nMyInt++;
	printf("nMyInt incremented again using the short way: %d", nMyInt);
	return 0;
}
/** console output:
* nMyInt as is: 2 
* nMyInt when incremented the long way: 3 
* nMyInt incremented again using the short way: 4 
*/

You can use this for other operators as well.

Code Equivalent To Description
i = i + 2 i += 2 Add 2 to my variable i
x = x-15 x -= 15 Subtract 15 to my variable x
share = share/4 share /= 4 Divide variable share by 4
j = j % 2 j %= 2 Perform mod 2 onto variable j

Keywords

Keywords have special meaning in C. These are reserved words that can't be used as identifiers. The common ones are: auto, else, long, switch, break, enum, register, typedef, case, extern, return, union, char, float, short, unsigned, const, for, signed, void, continue, goto, sizeof, volatile, default, if, static, while, do, int, struct, double.

If the Machine Project Specs/specifications were given to you at this point, then you might see that goto is not allowed. goto is a keyword that lets you jump to another part in your code. This isn't relevant to you now.

You may notice return 0; in the code samples in this note. This is so you can end the program

Separators

Separators are symbols in C that are used to separate tokens. Spaces, tabs, and newlines (or whitespaces) are not tokens themselves. colon (:), comma (,), and semi-colon (;) are also separators.

#include <stdio.h>
int main(){int nSample = 42;printf("This is my code\n");printf("Hello World!\n\n\n\n");printf("My Sample Variable: %d\n",nSample);return 0;}

(doesn't mean you should do this though.)