Programming Language A

Transcription

1 Programming Language A Takako Nemoto (JAIST) 30 October Takako Nemoto (JAIST) 30 October 1 / 29

2 From Homework 3 Homework 3 1 Write a program to convert the input Celsius degree temperature into Fahrenheight with 1 floating digit. 2 Write a such program s.t. it asks the elevator A s location (floor); the elevator B s location (floor); the elevator C s location (floor) and your current location (floor), and prints the closest elevator. Hint: Function abs. You should include stdlib.h. 3 See the next page. 4 Read ch.2-4 (pp ) of the textbook. Takako Nemoto (JAIST) 30 October 2 / 29

3 Homework 3 Rewrite the following using switch instead of if: int no; printf("input an integer: "); if(no % 2) printf("it is odd."); else printf("it is odd."); Takako Nemoto (JAIST) 30 October 3 / 29

4 Elevator problem Basically, there are two variations: If the closest elevator is not unique, answer ALL closest ones; or answer only one of them with some priority. Since I did not specified, both are fine. Almost all programs works well, only if we input POSITIVE floor number. How to modify for buildings with basements? Japanese floor counting system (...B2, B1, 1, 2, 3...) or European counting system (... -2, -1, 0, 1, 2,...)? Takako Nemoto (JAIST) 30 October 4 / 29

5 Some examples & re-submission for Homework 2, 3 See additional material. Re-submission of Homework 2 and 3 will be accepted by 5 November. Takako Nemoto (JAIST) 30 October 5 / 29

6 if and switch if is suitable for a simple case distinction. For the distinctions of many cases, if needs nests and so switch is simpler. #include <stdlib.h> #include <stdlib.h> int x = rand(); if(x % 4 == 0 x % 4 == 1) if(x % 4 == 0) printf("case 0"); else printf("case 1"); else if(x % 4 == 2) printf("case 2"); else printf("case 3"); int x = rand(); switch(x % 4){ case 0 : printf("case 0"); break; case 1 : printf("case 1"); break; case 2 : printf("case 2"); break; case 3 : printf("case 3"); break; Takako Nemoto (JAIST) 30 October 6 / 29

7 Loop: 2 ways of repeat a process do loop while loop and for loop Start Start Process 1 Process 1 Process 2 Condition Yes Process 2 Yes Condition No Process 3 Process 3 End No End Observation In do loop, Process 2 is done at least once. In while loop Process 2 might not be done. Takako Nemoto (JAIST) 30 October 7 / 29

8 do statement int no; do{ printf("%d ", no); no = no - 1; while (no >= 0); printf("\n"); Input a positive integer: The... part is loop body. It is repeated as long as the condition inside while (...) holds. Inside while is called control sequence. First, the executed once. part is Note that after once execution of..., the value of no is decreased by 1. If the new value of no satisfies no >= 0, then the... part is repeated once more. Takako Nemoto (JAIST) 30 October 8 / 29

9 while statement int no; while (no >= 0){ printf("%d ", no); no = no - 1; printf("\n"); Input a positive integer: If the condition inside while(...) holds, the part is executed. Note that the decision is made before executing loop body... is executed. Depending on the value of no, the part... is not executed at all. Therefore, you have to assign appropriate value to variables inside while(...). Otherwise, undefined value cause unexpected behavior. Takako Nemoto (JAIST) 30 October 9 / 29

10 do and while int no; do{ printf("%d ", no); no = no - 1; while (no >= 0); printf("\n"); int no; while (no >= 0){ printf("%d ", no); no = no - 1; printf("\n"); Input a positive integer: Input a positive integer: Takako Nemoto (JAIST) 30 October 10 / 29

11 do and while int no; do{ printf("%d ", no); no = no - 1; while (no >= 0); printf("\n"); int no; while (no >= 0){ printf("%d ", no); no = no - 1; printf("\n"); Input a positive integer: 0 0 Input a positive integer: 0 0 Takako Nemoto (JAIST) 30 October 11 / 29

12 do and while int no; do{ printf("%d ", no); no = no - 1; while (no >= 0); printf("\n"); int no; while (no >= 0){ printf("%d ", no); no = no - 1; printf("\n"); Input a positive integer: -1-1 Input a positive integer: -1 Takako Nemoto (JAIST) 30 October 12 / 29

13 while and for The following two programs behaves same as the previous one. int no, i; i = no; while (i >= 0){ printf("%d ", i); i = i -1; printf("\n"); Input a positive integer: int no, i; for (i = no; i >= 0; i = i -1){ printf("%d ", i); printf("\n"); Input a positive integer: Takako Nemoto (JAIST) 30 October 13 / 29

14 for statement int no, i; for (i = no; i >= 0; i = i -1){ printf("%d ", i); printf("\n"); for(a; B; C)... A is preprocessing. B is control sequence. C is post-processing. It can be written using while A while(b){... C Conversely, every while statement can be expressed by while. If no preprocessing is needed, it can be omitted. Takako Nemoto (JAIST) 30 October 14 / 29

15 Useful operators: Compound assignment operators By the way, sum = sum + t; means almost the same as sum += t; Such a operator is called a compound assignment operator. Compound assignment operators b has almost same meaning as a = b, is one of them: * / % + - << >> & ˆ Takako Nemoto (JAIST) 30 October 15 / 29

16 Useful operators: Postfixed increment & decrement Similarly cnt = cnt + 1; and cnt = cnt - 1; mean almost the same as, respectively, cnt++; and cnt--;. Exercise Verify that sum = sum + t and cnt = cnt +1 in the previous program can be replaced by sum += t and cnt++, respectively. Takako Nemoto (JAIST) 30 October 16 / 29

17 Useful operators: Postfixed increment & decrement Similarly cnt = cnt + 1; and cnt = cnt - 1; mean almost the same as, respectively, Warning! cnt++; and cnt--;. For a variable var, var++ alone acts the same as var = var + 1. But if it appears in some other statement like A(var);, then it acts as A(var); var = var + 1;. For example, printf("%d", var++); acts as Same as var--. printf("%d", var); var = var + 1; Takako Nemoto (JAIST) 30 October 16 / 29

18 Use of postfixed decrement operator The following program behave in the same way. int no; while (no >= 0){ printf("%d ", no--); printf("\n"); int no; while (no >= 0){ printf("%d ", no--); printf("\n"); Takako Nemoto (JAIST) 30 October 17 / 29

19 Example int retry; do { int no; printf("input an integer: "); if(no % 2) printf("it is odd.\n"); else printf("it is even.\n"); printf("continue? (yes = 0/no = 9): "); scanf("%d", &retry); while (retry == 0); Inside of do{... is repeated while the condition inside while(...) is satisfied. The variable no is used only in the do block, and so declared inside it. Takako Nemoto (JAIST) 30 October 18 / 29

20 Choose a valid number! int main(void) { int x = 0; do { printf("choose a nonnegative integer x < 3: "); scanf("%d", &x); while(x < 0 3 <= x); printf("you chose %d.", x); Choose a nonnegative integer x < 3: 4 Choose a nonnegative integer x < 3: 3 Choose a nonnegative integer x < 3: 2 You chose 2. Takako Nemoto (JAIST) 30 October 19 / 29

21 Example: Start hand, hand0, hand1 rand() generates a random integer. Using it, you can create a simple program for. rand() hand1 hand hand0 Yes No End Takako Nemoto (JAIST) 30 October 20 / 29

22 Multiple addition and the average int main(void){ int sum = 0; int cnt = 0; int retry; do{ int t; printf("input an integer: "); scanf("%d", &t); sum += t; cnt++; printf("continue? <yes = 0 / no = 9>: "); scanf("%d", &retry); while (retry == 0); printf("the sum of %d inputs ", cnt); printf("is %d and ", sum); printf("the average is %d.", (double)sum / cnt); While the user choose yes, the process is repeated, which allows unfixed number of inputs. cnt acts as a counter for the number of inputs. Recall that sum += t; cnt++ acts same as sum = sum + t; cnt = cnt + 1 Takako Nemoto (JAIST) 30 October 21 / 29

23 Another version of average int i = 0; int sum = 0; int num, temp; printf("number of items: "); scanf("%d", &num); while(i < num){ i = i + 1; printf("no.%d: ", i); scanf("%d", &temp); sum += temp; printf("total: %d\n", sum); printf("average: %.2f\n", (double)sum / num); If the number of items is 0, no loop process is executed. If you know the number of items in advance, this is easier to use than the previous one. (No need to choose yes.) Takako Nemoto (JAIST) 30 October 22 / 29

24 Useful operators: Prefixed increment & decrement i = i + 1; and i = i - 1; mean almost the same as, respectively, Warning! ++i; and ++i;. For a variable var, ++var alone acts the same as var = var + 1. But if it appears in some other statement like A(var);, then it acts as var = var + 1;. A(var); For example, printf("%d", ++var); acts as var = var + 1; printf("%d", var); Same as --var. Takako Nemoto (JAIST) 30 October 23 / 29

25 Useful operators: Prefixed increment & decrement i = i + 1; and i = i - 1; mean almost the same as, respectively, ++i; and ++i;. Exercise Run the following program and verify the behaviors of each operators #include<stdio.h> int i = 0; int j = 0; int k = 0; int l = 0; printf("i=%d ", ++i); printf("j=%d\n", j++); printf("i=%d ", i); printf("j=%d\n", j); printf("k=%d ", ++k); printf("l=%d\n", l++); printf("k=%d ", k); printf("l=%d\n", l); Takako Nemoto (JAIST) 30 October 24 / 29

26 Use of prefixed increment operator int i = 0; int sum = 0; int num, temp; printf("number of items: "); scanf("%d", &num); while(i < num){ printf("no.%d: ", ++i); scanf("%d", &temp); sum += temp; printf("total: %d\n", sum); printf("average: %.2f\n", (double)sum / num); Takako Nemoto (JAIST) 30 October 25 / 29

27 Example: Print the input number of * Note that int no; while (no-- > 0) putchar( * ); putchar( \n ); while (no-- > 0) putchar( * ); is same as while (no > 0) no = no - 1; putchar( * ); The function putchar is to print a single character *. Use single quotation. Takako Nemoto (JAIST) 30 October 26 / 29

28 Example: Prints all power of 2 below the input (Ex. 4-7) int no, i; for(i = 1; i < no; i *= 2){ printf("%d ", i); Set the value i as 0 before starting the loop. If i < no hold, then printf("%d ", i) and i *= 2 are executed. Takako Nemoto (JAIST) 30 October 27 / 29

29 /* Decide prime or not*/ int no, i; do{ if (no <= 0) printf("do not input any non-negative integer!"); while (no <= 0); for(i = 2;!(no % i == 0); i++); /*empty statement*/ if (!(i == no)){ puts("it is not prime."); printf("the least nontrivial factor is %d.", i); else puts("it is prime."); Takako Nemoto (JAIST) 30 October 28 / 29

30 Today s homework 1 Write a program which answers, for the input of the year and month, it answers how many days it has. For example, February 2018 has 28 days. Do not forget bissextile years having 29 February, which are years s.t. divisible by 4 but not by 100 or; divisible by Rewrite the program at the right of the page of do and while (p.11) so that it does not output \n for any negative input. Simplify it with the postfixed decrement operator. 3 Write a program s.t., for a positive integer-valued input, it prints all positive factors of it in ascending order. Use for. 4 (optional) Do any exercise you like, exept for the one explained in the lecture. 5 (optional) 3 Send the programs as attached files to me via , with the title Homework Lecture4 by the next lecture. Please make sure to include your name and student ID number. Takako Nemoto (JAIST) 30 October 29 / 29