Conditional Statements in C

Introduction

Imagine a fork in the road, where each route leads to a different place.

In the same way, conditionals allow our program to take many paths, and thus, lead to many unique outcomes.

So...

if (you're interested in learning C)
{
	// continue reading
}

Booleans and Common Conditionals

Inherently, all conditional statements rely on some boolean expression that evaluates to either true or false.

For instance:

#include <stdio.h>

int main(void)
{
	// retrieves user input, storing the value at the address of x
	scanf("%d", &x);

	// returns -1 if the number the user has entered was not 3
	if (x != 3)
		return -1;

	return 0;
}

Here, the boolean expression was x != 3, which could evaluate to true or false depending on what the user enters. Notice how if the conditional was false and x was indeed 3, the if would be skipped and 0 would be returned.

Some fairly common examples of conditionals include:

• if

if (boolean-statement)
{
	...
}

• if-else

  • where else is a catch-all and requires no boolean expression, unlike if

  • else only runs if the if statement was false, and vice versa

if (boolean-statement)
{
	...
}
else
{
	...
}

• if-else if ... - else

  • else if is essentially an else with a boolean expression

  • else if only runs if the statement previous to it was false

  • can be a chain of else if statements

  • *does not need to end with an else

if (boolean-statement)
{
	...
}
else if (boolean-statement)
{
	...
}
else if (boolean-statement)
{
	...
}
else if (boolean-statement)
{
	...
}
else
{
	...
}

Switch( ) Statement

switch( ) statements are very similar to if-else if-else chains, in that they result in different outcomes based on their input.

They can be, however, more dynamic, as multiple statements can execute after one another like a cascade.

#include <stdio.h>

int main(void)
{
	scanf("%d", &x);

	switch(x)
	{
		case 1:
			printf("One!\n");
			break;
		case 2:
			printf("Two!\n");
			break;
		case 3:
			printf("Three!\n");
			break;
		default:
			printf("No cases were met!\n");
			break;
	}

	return 0;
}

Here, with x as input, the switch( ) statement compared the value stored in x with each value following each case. For example, if I had entered 1, the program would print "One!" If I hadn't entered any of the three case values, the program would resort to the default.

So how is this different from traditional conditionals?

Well, notice how we had to use a break statement after each print() in order to stop the cascading behavior mentioned before.

Remove these breaks, and should the user enter 2, the program would output:

One!
Two!
Three!
No cases were met!

You can imagine how this type of conditional could be useful in things like a countdown.

Shortcuts...

For writing trivially short conditional statements, C is equipped with what is called a ternary operator ( ? : ).

I could rewrite:

const int num = 2;

// assume the user enters an integer guess
scanf("%d", &userGuess);

int points;
if (userGuess == num)
{
	points = 1;
}
else
{
	points = 0;
}

as:

const int num = 2;

// assume the user enters an integer guess
scanf("%d", &userGuess);

int points = (userGuess == num) ? 1 : 0;

The ternary operator allows us to check the first boolean expression (userGuess == num) and if that is true, the variable holds the value after the ( ? ). If that expression is false, the variable holds the value after the ( : ).

Final Thoughts

Hopefully by the end of this article you've at least gained a brief idea of the different types of conditional statements and when to them. Thanks for reading!

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