Basics of C

This post will briefly cover the Basics of C. This is a summary of what I consider important. Let’s start from the beggining.

¿How to print in C?

#include <iostream>

main () {
	
	printf("Hello World");
}

¿How does C input/output data?

We’re able to do it thanks to the standard input/output library <stdio.h>.

#include <stdio.h>

Types of Data

Ways to print a floating point

example : 

	while (fahr <= upper) {
	celsius = (5.0/9.0) * (fahr-32.0);
	printf("%3.0f %6.1f\n", fahr, celsius);
	fahr = fahr + step;
	

The for statement

x=0
for (i=0 ; i<=100 ; i++){
	x++;
	printf(x);
}

i=0 represents the start of the loop. i<=100 means that i won’t go higher than 100. i++ means that the increment will be +1. If we wanted a higher number, we could write i= i + x been x the increment that we want.

While loop

x=0
while ( i<=100 ) {
	
	x++;
	printf(x);

}

i<=100 will be the condition of the while loop. The code will be repeating if the condition returns True. If the condition returns False, the loop will stop iterating.

Symbolic Constants

If we wanted to assign a number (for example) to a variable that won’t change in the future, its a better idea to define it beforehand.

#include <iostream>

#define MINIMUMAGE 18 /* minimum age to enter to a pub * /

#define YEAR 365 /* number of days in a year * /

Character Input and Output

To input and print a single character (char) we are provided with getchar and putchar functions.

getchar allows us to receive a char from the user.

putchar prints the character.

/* we are inputting a letter to a variable */
letter = getchar();
/* now lets print it */
putchar(letter);

File Copying

Let’s say we want to loop until an End of File is reached. For that, C includes a special value, EOF. This value is unique, so it can’t be confused with any real character. EOF is an integer defined in <stdio.h>, so we cannot store it in a char, we’re going to use int.

main()
{
int c;
c = getchar();
while (c != EOF) {
putchar(c);
c = getchar();
}
}

If you try this in your compiler, entering the value EOF won’t do the job. You must press F6 or Ctrl+Z, that’s how you enter EOF on Windows.

Array

A really useful way to store more than a value in a variable.

main(){
	int fourNumbers[3];

	fourNumbers[0]= 1
	fourNumbers[1]= 2
	fourNumbers[2]= 3
	fourNumbers[3]= 4

}

Functions

We’ve been using built-in functions as getchar() , putchar(). It’s time to make our own functions.

Functions have three parts: Prototype, Call and Declaration.

Prototype: Informs compiler about function name, functions parameters and what it’s going to return. Prototype always must be written above the main function. Specifying the parameters names, are optional.

Call: Informs compiler we’re going to use the function.

Declaration: Contains all the statements to be executed.

#include <stdio.h>

int power (int, int) /* Prototype of power function */

main(){

printf( "%d", power(2,4) );  /* Calling and printing the function*/

}

/* Declaring the function */
int power(int base, int exponent)
{
	int result,i;
	result=1;
	
 	for (i=0 ; i < exponent ; i++){
 	
 	result = result*base;
 	
 	};
 	
 	return result;
 }

Type Conversions

In general, if an operator like + or * that takes two operands (a binary operator) has operands of different types, the ‘‘lower’’ type is promoted to the ‘‘higher’’ type before the operation proceeds

For Example: If we sum an int to a float, the int will be converted to a float.

Hopefully, C does this by itself and let us focus on more important problems.

Increment and Decrement Operators

C includes two special operators ++ and --, they act as an adder and subtractor respectively. These operators can be used as prefix or postfix operators.

int a,b,c;

c=12

while (a > b){

	b++; // Adds 1 to b.
	--c; // Subtracts 1 from c
}

Conditional Expressions

The statements will compute the maximum between a and b.

int a=5;
int b=3;
int result;

if (a > b) {
	result = a;
}
else {
	result = b;
}

return result;

There’s an alternative version for the if/else statement, the Ternary Operator :?

result = a > b :? a : b ;

It’s true that the traditional if/else statement will be more readable for people watching our code, but it’s good to know about :? existence.

Joaquin Ipar

I'm Joaquin Ipar, Systems Engineering Student