A for loop is a type of control flow statement that repeatedly runs a section of code until a condition is satisfied.

for (int i = 0; i < 3; ++i) {
    printf("%d", i);
}

Example of a for loop that prints "012" in C

Low Level Implementation

At the assembly level, for loops are implemented using conditional and unconditional jumps. The compiler translates the initialization, condition check, increment, and loop body into equivalent jump-based control flow.

<init>
loop_start:
    'evaluate condition
    goto end_loop if not <continue_condition>

    'loop body
    ...

    'increment and repeat
    <step>
    goto loop_start
end_loop:

Example

for (int i = 0; i < 3; ++i) {
	// ...
}

.pos 0x1000
	# <init>
	ld $i, r0         # r0 = &i
	ld (r0), r0       # r0 = i
	ld $-3, r1        # r1 = 3
	
	loop_start: 
		mov r0, r2    # r2 = i
		add r1, r2    # r2 = i - 3 (allows us to use beq)
		
		# evaluate condition
		beq r1, end_loop # go to just after loop
		
		# loop body
		
		# increment and repeat
		inc r0
		br loop # go to start of loop	

	end_loop: 

.pos 0x2000
	i:      .long 0