1 00:00:04,939 --> 00:00:08,900 So now that we've seen how to use the debugger to step through our code line by line, 2 00:00:08,900 --> 00:00:11,760 let's explore if statements a bit more. 3 00:00:11,760 --> 00:00:15,180 So I'm going to continue with the project we set up for this section of 4 00:00:15,180 --> 00:00:21,680 the course - Program Flow. I'm going to create a new python file and we're going to call that guessing game. 5 00:00:26,000 --> 00:00:29,140 Alright. Now I'm going to start this up very simply 6 00:00:29,140 --> 00:00:32,680 but we'll improve it as we go along. Firstly, I'm going to start by binding 7 00:00:32,720 --> 00:00:36,560 a variable to the answer. Now the answer will always be five at the moment 8 00:00:36,560 --> 00:00:42,000 and that's a bit boring but we'll improve the program later. So answer = 5 9 00:00:42,000 --> 00:00:45,600 So next I want to print a prompt to let the user know what they're entering, 10 00:00:45,600 --> 00:00:49,670 and then we'll use the input function to get their input. So on line 3 I'm gonna 11 00:00:49,670 --> 00:00:58,360 type print parenthesis double quotes, Please guess a number between one and ten. 12 00:00:58,360 --> 00:01:03,340 We'll put a colon and a space there, then we've got that closing double quote and right parenthesis. 13 00:01:03,340 --> 00:01:08,180 Then we're going to accept the input by typing guess equals int 14 00:01:08,180 --> 00:01:13,820 left parentheses input, left and right parentheses and then a closing right parenthesis. 15 00:01:13,820 --> 00:01:17,240 Now I haven't provided a prompt this time. We're printing a message on 16 00:01:17,240 --> 00:01:20,520 line three which tells the player what the program's expecting them to do. 17 00:01:20,520 --> 00:01:24,580 Line four uses the input function without a prompt, but we still need the opening and 18 00:01:24,590 --> 00:01:28,970 closing parentheses after it, as you saw me type. As before, we're using the int 19 00:01:28,970 --> 00:01:33,380 function to convert their input to an integer. All input is stored as a string, 20 00:01:33,380 --> 00:01:37,500 but here we want to deal with numbers. So on line 4, we're actually binding the 21 00:01:37,500 --> 00:01:41,460 name guess to the integer value that we've converted to an integer. 22 00:01:41,460 --> 00:01:44,980 So make sure you only entered valid numbers when we run the program. We'll be looking at 23 00:01:44,980 --> 00:01:47,640 how to cope with invalid input later in the course. 24 00:01:47,640 --> 00:01:51,320 Alright though, now it's time to see if the players guess was correct. Now here, 25 00:01:51,320 --> 00:01:55,160 when we run the program, there's three possible outcomes. The guess could be too 26 00:01:55,160 --> 00:02:00,110 low, it could be too high or they could have guessed it correctly. What we want 27 00:02:00,110 --> 00:02:05,000 to do first is test for a too low guess. We'll do that first and we'll do that on 28 00:02:05,040 --> 00:02:14,440 line 6 by typing if guess is less than answer : then in parentheses, sorry print, then 29 00:02:14,440 --> 00:02:20,440 parenthesis on line 7, double quotes, Please guess higher. Then we've got our 30 00:02:20,440 --> 00:02:25,400 closing double quote and right parenthesis. So basically, if their guess is less than the 31 00:02:25,400 --> 00:02:29,660 answer, we print a message asking them to guess higher. Now there's a bit more we 32 00:02:29,660 --> 00:02:32,959 need to do here but we'll come back to that. Before we do though, let's add a 33 00:02:32,960 --> 00:02:37,700 test for the guess being too high. Now we can do that using elif. So I'm here on 34 00:02:37,740 --> 00:02:43,940 line 8, I'm going to type elif guess. This time I'm going to type greater than 35 00:02:43,940 --> 00:02:48,100 answer : Then we're going to print on line 9, 36 00:02:48,100 --> 00:02:54,700 parenthesis double quote, Please guess lower. Then we've got our closing double 37 00:02:54,700 --> 00:02:59,440 quote and right parenthesis. Now you might think that we can just use if there, and 38 00:02:59,440 --> 00:03:04,620 you often can, but I'm going to discuss why that's sometimes not a good idea, shortly. 39 00:03:04,620 --> 00:03:09,139 Alright, so if the condition on line 6 is false, the condition on line 40 00:03:09,140 --> 00:03:13,400 8 is tested, and if that evaluates to true, in other words, if their guess is 41 00:03:13,400 --> 00:03:18,100 greater than the answer, then we print the message Please guess lower. So that's 42 00:03:18,109 --> 00:03:21,799 two of the three possible outcomes dealt with. We're checking for the guess being 43 00:03:21,800 --> 00:03:26,360 less than the answer, and for it being greater than the answer, so far. If both 44 00:03:26,400 --> 00:03:30,260 those conditions are false, then the guess must be equal to the answer. 45 00:03:30,260 --> 00:03:33,640 In other words, they've guessed correctly. So therefore, we can handle everything else 46 00:03:33,640 --> 00:03:38,560 here using else. So we're going to type else: on line 10, and print a message, 47 00:03:38,560 --> 00:03:44,820 print parenthesis double quote, You got it first time, then we've got a closing 48 00:03:44,820 --> 00:03:50,060 double quote and right parenthesis. So basically, the message on line 11 is only 49 00:03:50,060 --> 00:03:52,909 going to be printed if both the conditions on line 6 and line 8 50 00:03:52,909 --> 00:03:58,720 evaluate to false. Because else picks up everything else, it must come after the 51 00:03:58,720 --> 00:04:04,060 if and elif blocks. elif must follow an if, and all elif blocks have to appear 52 00:04:04,060 --> 00:04:08,000 before the else block, if there is one. Right, so let's run the program a few 53 00:04:08,000 --> 00:04:13,120 times to check that it's working. I'm gonna run it now. Now first I'm gonna 54 00:04:13,129 --> 00:04:17,959 enter my guess as 4. Remember to click into the run pane, as I just did, before 55 00:04:17,959 --> 00:04:22,520 typing your guess. We get the message "Please guess higher", which is correct because 56 00:04:22,520 --> 00:04:27,540 obviously 4 is less than 5. I'm gonna run it again, 57 00:04:27,540 --> 00:04:32,680 and this time I'm gonna type a higher value, 8. You can see we've got the output "Please 58 00:04:32,680 --> 00:04:37,600 guess lower", which is also correct. 8, of course, is more or higher than 5. 59 00:04:37,600 --> 00:04:41,380 The third test is when the guess is correct, so I'm going to run that again, 60 00:04:41,380 --> 00:04:46,140 and this time I'm going to type in the value 5, and we've got the message "You got it 61 00:04:46,140 --> 00:04:50,820 first time" on screen. So run the program a few times with different guesses to 62 00:04:50,820 --> 00:04:54,220 make sure it works, and in the next video what we'll do is, we'll run the program 63 00:04:54,220 --> 00:04:59,670 in the debugger to check what it's doing. See you in the next video.