enter an arithmetic operation (ex. 5*4) in c

Question

I am trying to make a program that if the user gives a whole arithmetic operation from the keyboard ex 5*4 or 5/7 it will interpret the operation ex *, /, +, or - and print the result. How can I read the whole operation without the user pressing enter everytime he puts a number or a symbol ex * or / and put them in 3 variables? I tried using:

printf("give an operation")
scanf("%d%c%d",&num_1,&c,&num_2)

but I want to do with:

c=getchar()

So you want to manually parse numbers, even though we have `scanf` that can do that? Why? — Šimon Tóth, Nov 13 '12 at 10:30
If you want to do it manually, read more about [lexical analysis](http://en.wikipedia.org/wiki/Lexical_analysis) and [parsing](http://en.wikipedia.org/wiki/Parsing). — Some programmer dude, Nov 13 '12 at 10:32
i just dont want the program to wait the user to press enter after number 1 ,symbol and number 2 — user1809300, Nov 13 '12 at 10:40
So you want the user to enter three tokens (2 numbers and an operator in between) and *then* press enter? If so, `scanf` will work just fine. — jrok, Nov 13 '12 at 10:44
i want to use scanf for numbers and getchar for symbol but i dont want the user to press enter after every input — user1809300, Nov 13 '12 at 10:45
Does this http://stackoverflow.com/questions/9329406/evaluating-arithmetic-expressions-in-c/9329509#9329509 help? — Henrik, Nov 13 '12 at 10:50
@Let_Me_Be "understand the operation ex * / + or - and print the result to user". `sscanf` doesn't evaluate the result of an arithmetic operation. — Henrik, Nov 13 '12 at 11:00
@Henrik Yeah, sorry, I didn't read it properly, so not `sscanf` but `strtol`. — Šimon Tóth, Nov 13 '12 at 11:02
In this case i don't recommend you to use getchar, cause then you won't be able to scan numbers of more than 2 digits (I mean you can but it will be a bit harder). — Alberto Bonsanto, Nov 13 '12 at 11:04

score 2 · Answer 1 · answered Nov 13 '12 at 10:56

If I understand your question and comments correct, you want to read a line of input from the user, where the user enters an expression and uses the Enter key to end the expression?

Then using scanf should work fine. You could also use fgets to get the line, and the use sscanf for the parsing.

MOHAMED · Answer 2 · 2012-11-13T16:01:56.907

-1

scanf("%d %[*+-/] %d", &numA, op, &numB);

op should be defined as char array: char op[2];

Explanation

%[+-*/] : this means that you expect for %op the character + or - or * or /

edited Nov 13 '12 at 16:01

answered Nov 13 '12 at 10:32

MOHAMED

41,599
58
163
268

can you please explain how does this work ? – user1809300 Nov 13 '12 at 10:34
I update my answer with the right reg expression for scanf – MOHAMED Nov 13 '12 at 10:42
can you explain to me these %[^+-*/] %[+-*/] %s – user1809300 Nov 13 '12 at 10:44
i am not that experiencced with c and i cant find this somewhere – user1809300 Nov 13 '12 at 10:45
What problem is this answer supposed to solve? How is this better than what the OP had? – interjay Nov 13 '12 at 10:50
could you explain the downvote ? the answer is correct and it responds to the user1809300 question – MOHAMED Nov 13 '12 at 11:00
@interjay: It's not my problem if you do not understand the user1809300 question – MOHAMED Nov 13 '12 at 11:01
@MohamedKALLEL You are not even reading numbers. You are reading strings. – Šimon Tóth Nov 13 '12 at 11:04
@Let_Me_Be you are right I will update my answer – MOHAMED Nov 13 '12 at 11:05
He wants to store numbers, not variables so letters should be excluded. – Alberto Bonsanto Nov 13 '12 at 11:15
1

@MohamedKALLEL `atoi` doesn't report failures, your code is inferior to `scanf("%d%c%d",&num1,&op,&num2);` – Šimon Tóth Nov 13 '12 at 11:17
@Let_Me_Be alternate solution? – MOHAMED Nov 13 '12 at 11:25
@MohamedKALLEL You know, it's kind of pathetic not to even read the question you are answering. – Šimon Tóth Nov 13 '12 at 11:29

enter an arithmetic operation (ex. 5*4) in c

2 Answers2