Given a year, report if it is a leap year.
The tricky thing here is that a leap year in the Gregorian calendar occurs:
on every year that is evenly divisible by 4 except every year that is evenly divisible by 100 unless the year is also evenly divisible by 400
For example, 1997 is not a leap year, but 1996 is. 1900 is not a leap year, but 2000 is.
If your language provides a method in the standard library that does this look-up, pretend it doesn't exist and implement it yourself.
Though our exercise adopts some very simple rules, there is more to learn!
For a delightful, four minute explanation of the whole leap year phenomenon, go watch this youtube video.
JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
# # Test is_leap_year with some examples # # s0 - num of tests left to run # s1 - address of input word # s2 - address of expected output word # s3 - input word # s4 - output word # # is_leap_year must: # - be named is_leap_year and declared as global # - read input integer from a0 # - follow the convention of using the t0-9 registers for temporary storage # - (if it wants to use s0-7 then it is responsible for pushing existing values to the stack then popping them back off before returning) # - write boolean result to v0 .data n: .word 7 # number of test cases ins: .word 1996, 1997, 1998, 1900, 1800, 2400, 2000 # input years outs: .word 1, 0, 0, 0, 0, 1, 1 # expected result failmsg: .asciiz "failed for test input: " okmsg: .asciiz "all tests passed" .text runner: lw $s0, n la $s1, ins la $s2, outs run_test: lw $s3, 0($s1) # read input from memory move $a0, $s3 # move it to a0 jal is_leap_year # call subroutine under test move $v1, $v0 # move return value in v0 to v1 because we need v0 for syscall lw $s4, 0($s2) # read expected output from memory bne $v1, $s4, exit_fail # if expected doesn't match actual, jump to fail addi $s1, $s1, 4 # move to next word in input addi $s2, $s2, 4 # move to next word in output sub $s0, $s0, 1 # decrement num of tests left to run bgt $s0, $zero, run_test # if more than zero tests to run, jump to run_test exit_ok: la $a0, okmsg # put address of okmsg into a0 li $v0, 4 # 4 is print string syscall li $v0, 10 # 10 is exit with zero status (clean exit) syscall exit_fail: la $a0, failmsg # put address of failmsg into a0 li $v0, 4 # 4 is print string syscall move $a0, $s3 # set arg of syscall to input that failed the test li $v0, 1 # 1 is print int syscall li $a0, 1 # set exit code to 1 li $v0, 17 # terminate with the exit code in $a0 syscall # # Include your implementation here if you wish to run this from the MARS GUI. # .include "impl.mips"
# take an integer representing a year and return a boolean # response for whether that year is a leap year or not # a0::Unsigned -> v0::Boolean is_leap_year: li $t0, 400 divu $a0, $t0 mfhi $t0 beq $t0, $0, true li $t0, 100 divu $a0, $t0 mfhi $t0 beq $t0, $0, false li $t0, 4 divu $a0, $t0 mfhi $t0 beq $t0, $0, true false: li $v0, 0 jr $ra true: li $v0, 1 jr $ra
A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.
Here are some questions to help you reflect on this solution and learn the most from it.