Program to emulate calculator

This is a discussion on Program to emulate calculator within the C Programming forums, part of the General Programming Boards category; Hi all, i was told to do up a program to emulate a calculator (+-*/ functions) but i am unable ...

  1. #1
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    Program to emulate calculator

    Hi all,

    i was told to do up a program to emulate a calculator (+-*/ functions) but i am unable to get the program to show my answer.
    attached is the program i typed. can someone help me out?

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    double Addition(double num1, double num2){
        return num1+num2;
    }
    double Subtraction(double num1, double num2){
        return num1-num2;
    }
    double Multiplication(double num1, double num2){
        return num1*num2;
    }
    double Division(double num1, double num2){
        return num1/num2;
    }
    main (int argc, char *argv[]){
        char sign;
        double first_num, second_num;
        printf("Type 2 numbers and an operation\n");
        scanf("%lf %c %lf", &first_num, &sign, &second_num);
    
        if (&sign == "+")
            printf("%f\n", Addition(first_num, second_num));
     else if (&sign == "-")
            printf("%f\n", Subtraction(first_num, second_num));
     else if (&sign == "*")
            printf("%f\n", Multiplication(first_num, second_num));
     else if (&sign == "/")
            printf("%f\n", Division(first_num, second_num));
    }

  2. #2
    Technical Lead QuantumPete's Avatar
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    When you do (&sign == "+") you're actually performing an address comparison. You're comparing the address of the variable sign (which you get by prepending the &) with the address of the global string literal "+".
    What you really want is a character comparison. So you need to take the variable itself and compare agains the *character* +, which you do by using single quotes.
    Also two other things to note are that you are missing the curly braces on your if and else if statements and that the format specifier in your printf statements is missing the l (ell) that makes it print out a double instead of a float.

    QuantumPete
    "No-one else has reported this problem, you're either crazy or a liar" - Dogbert Technical Support
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  3. #3
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    Quote Originally Posted by QuantumPete View Post
    that the format specifier in your printf statements is missing the l (ell) that makes it print out a double instead of a float.
    Whilst the rest of your post is indeed correct, this part is not.
    1. All floating point values are promoted to double when passed to var-args functions (and functions with unspecified arguements - old-style code). Thus %f is used for float and double - since they are all double anyways.
    2. %lf is used in some compilers (c99) to indicate "long double", which would lead to erroneous output. In other compilers, %lf _may_ mean double, but in others it will be "unknown" [and thus in the clearly undefined behaviour arena].

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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    it finally works!
    haha thanks to the both of u pete and mats!

  5. #5
    Technical Lead QuantumPete's Avatar
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    Quote Originally Posted by matsp View Post
    Whilst the rest of your post is indeed correct, this part is not.
    1. All floating point values are promoted to double when passed to var-args functions (and functions with unspecified arguements - old-style code). Thus %f is used for float and double - since they are all double anyways.
    2. %lf is used in some compilers (c99) to indicate "long double", which would lead to erroneous output. In other compilers, %lf _may_ mean double, but in others it will be "unknown" [and thus in the clearly undefined behaviour arena].

    --
    Mats
    You live and learn. I was sure thaf %f is float and %lf is double...
    "No-one else has reported this problem, you're either crazy or a liar" - Dogbert Technical Support
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  6. #6
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by QuantumPete View Post
    You live and learn. I was sure thaf %f is float and %lf is double...
    For scanf, it is. For printf, it isn't.

  7. #7
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by QuantumPete View Post
    Also two other things to note are that you are missing the curly braces on your if and else if statements...
    Oh, but it's not required. It's optional.
    More like it's recommended. But then again, perhaps not, because it takes space.
    There's no easy answer to that question, but it certainly isn't required.

    Oh and you're using implicit main. That's bad.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  8. #8
    Technical Lead QuantumPete's Avatar
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    Quote Originally Posted by Elysia View Post
    Oh, but it's not required. It's optional.
    True, but it's better to have them and not need them, then to need them and not have them

    QuantumPete
    "No-one else has reported this problem, you're either crazy or a liar" - Dogbert Technical Support
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  9. #9
    Technical Lead QuantumPete's Avatar
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    Quote Originally Posted by tabstop View Post
    For scanf, it is. For printf, it isn't.
    [sarcasm]Well of course, that makes sense, two functions from the same library using the same format specifier meaning different things. [/sarcasm] There are days I hate C

    QuantumPete
    "No-one else has reported this problem, you're either crazy or a liar" - Dogbert Technical Support
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  10. #10
    CSharpener vart's Avatar
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    same format specifier meaning different things
    Not much sense to do different format specifiers for float and double in printf while both are passed as double

    scanf is other story...
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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    Hi, I also need help in the code... after trying out with the modified code, i still receive error upon running... and also unable to get program to show the answer
    Can anyone help? Need it to be done urgently... ):

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    double Addition(double num1, double num2){
        return num1+num2;
    }
    double Subtraction(double num1, double num2){
        return num1-num2;
    }
    double Multiplication(double num1, double num2){
        return num1*num2;
    }
    double Division(double num1, double num2){
        return num1/num2;
    }
    main (int argc, char *argv[]){
        char operator;
        double first_num, second_num;
        printf("Type 2 numbers and an operator\n");
        scanf("&#37;f %c %f", &first_num, &operator, &second_num);
    
        if (&operator == '+') {
            printf("%f\n", Addition(first_num, second_num));
     }else if (&operator == '-') {
            printf("%f\n", Subtraction(first_num, second_num));
     }else if (&operator == '*'){
            printf("%f\n", Multiplication(first_num, second_num));
     }else if (&operator == '/'){
            printf("%f\n", Division(first_num, second_num));
    }
    }

  12. #12
    and the Hat of Guessing tabstop's Avatar
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    And you didn't read Pete's first response because why?

  13. #13
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    eh it's because I don't really understand.. i'm totally new to this..
    and i did add in the brackets to if and if else statements, changing the " " to ' ' , &#37;If to %f
    it still don't work..
    Last edited by Zihui02; 09-04-2008 at 09:48 AM.

  14. #14
    and the Hat of Guessing tabstop's Avatar
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    And if you do the other bit mentioned, namely getting rid of &, what happens?

    And if you don't understand what he said, look up the words in the index of your textbook to get a brush-up on the vocabulary.

  15. #15
    C++まいる!Cをこわせ! Elysia's Avatar
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    The & operator takes the ADDRESS of something and the ADDRESS of something generates an extra indirection, ie char becomes char*, and char* is not the same as char. The end.
    And you still haven't fixed main either.
    But do say, do you have a book or is it a course from where you're teaching yourself?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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