A conditional is a type of control flow that branches based on one or more expressions.

int a;
scanf("%d", &a);

if (a % 2 == 0) {
	printf("%d is even", a);
} else {
	printf("%d is odd", a);
}

Example of a conditional statement that checks whether a number is even or odd

Low Level Implementation

At the assembly level, conditionals are implemented using jumps as well as logic for the condition. The compiler translates the boolean expression of the condition into arithmetic ones depending on the architecture.

<init>
'conditional setup
goto then if <condition>
else:
	'alternative body
    goto end_if
then:
	'consequent body
end_if:

Example

int a = 5;
int b = 2;

if (a > b) {
	// consequent
} else {
	// alternative
}

.pos 0x1000
	# <init>
	ld $a, r0         # r0 = &a
	ld (r0), r0       # r0 = a
	ld $b, r1         # r1 = &b
	ld (r1), r1       # r1 = b
	
	mv r1, r2         # r2 = b
	not r2            # r2 = !b
	inc r2            # r2 = -b
	
	add r0, r2        # r2 = a-b
	
	bgt r2, then      # a-b > 0 => goto then
	
	else: 
		# alternative
		br end_if
	
	then:
		# consequent

	end_if: 

.pos 0x2000
	a:      .long 5
	b:      .long 2