Thread: simple calculator: what's wrong with this code?

  1. #1
    Registered User
    Join Date
    Apr 2014
    Posts
    12

    Unhappy simple calculator: what's wrong with this code?

    Pls help
    Thank you

    Code:
    /* A simple program in which the user picks 2 numbers and does mathematical operation ( +, -, * or / )  */
    
    
    #include <stdio.h>
    #include <stdlib.h>
    
    
    int main()
    {
        int num1;
        int num2;
        int rsult = 0;
        char oprtn;
        printf("Enter the first number: ");
        scanf("%i", &num1);
        printf("Enter the second number: ");
        scanf("%i", &num2);
        printf("Choose an operator (a/s/m/d): ");
        scanf("%s", &oprtn);
        switch(oprtn)
        {
        case 'a':
            rsult = num1 + num2;
            printf("Your result is %i", rsult);
            break;
    
    
        case 's':
            rsult = num1 - num2;
            printf("Your result is %i", rsult);
            break;
    
    
        case 'm':
            rsult = num1 * num2;
            printf("Your result is %i", rsult);
            break;
    
    
        case 'd':
            rsult = num1 / num2;
            printf("Your result is %i", rsult);
            break;
        }
    
    
    
    
        getch();
    }

    test:
    num1 = 5
    num2 = 6
    oprtn = a
    gives a result of 5

  2. #2
    Registered User
    Join Date
    May 2009
    Posts
    3,864
    This is NOT defined; it could do anything. (When oprtn is of char type)

    Code:
    scanf("%s", &oprtn);
    I suggest trying; note the space before the % is needed to skip newline/space.
    Code:
    scanf(" %c", &oprtn);
    Tim S.
    "...a computer is a stupid machine with the ability to do incredibly smart things, while computer programmers are smart people with the ability to do incredibly stupid things. They are,in short, a perfect match.." Bill Bryson

  3. #3
    Registered User Alpo's Avatar
    Join Date
    Apr 2014
    Posts
    877
    There are a few things wrong, but it's helpful to include what the output is, as well as the input (In this case input is pretty obvious).

    You are using a char to store a string format, it's probably easier to use a %c format. Also, you will need to use float's for division (it commonly produces decimal leftover). The getch() function is from conio.h, so you will need to include it (getchar() would probably be more portable though).

  4. #4
    Registered User
    Join Date
    Apr 2014
    Posts
    12
    OK forget using char.
    Even if I use int, it ALWAYS gives me the the value of x as the output
    Code:
    /* A simple program in which the user picks 2 numbers and does mathematical operation ( +, -, * or / )  */
    
    #include <stdio.h>
    #include <stdlib.h>
    
    int main()
    {
        int x;
        int y;
        int rsult = 0;
        char oprtn;
        printf("Enter the first number: ");
        scanf("%i", &x);
        printf("Enter the second number: ");
        scanf("%i", &y);
        printf("Choose an operator\n");
        printf("1=add, 2=sub, 3=mult, 4=div\n");
        scanf("%i", &oprtn);
        switch(oprtn)
        {
        case 1:
            rsult = x+y;
            printf("Your result is %i", rsult);
            break;
    
        case 2:
            rsult = x-y;
            printf("Your result is %i", rsult);
            break;
    
        case 3:
            rsult = x*y;
            printf("Your result is %i", rsult);
            break;
    
        case 4:
            rsult = x/y;
            printf("Your result is %i", rsult);
            break;
        }
    
        return 0;
    }

  5. #5
    Registered User
    Join Date
    Apr 2014
    Location
    Pakistan
    Posts
    7
    Don't go in too deep with %i, just use %d.

  6. #6
    Registered User
    Join Date
    Jun 2011
    Posts
    4,509
    Even if I use int, it ALWAYS gives me the the value of x as the output
    Are you getting warnings when you compile?

    Code:
    /*
    ||=== scrap_c, Debug ===|
    main.c||In function 'main':|
    main.c|18|warning: format '%i' expects type 'int *', but argument 2 has type 'char *'|
    ||=== Build finished: 0 errors, 1 warnings ===|
    */
    Also, why are you trimming your variable names? "result" is much easier to read/write/remember than "rsult" - ditto for "operation" versus "oprtn".

  7. #7
    Registered User
    Join Date
    Apr 2014
    Posts
    12
    Edit:
    Code:
    /* A simple program in which the user picks 2 numbers and does mathematical operation ( +, -, * or / )  */
    
    
    #include <stdio.h>
    #include <stdlib.h>
    
    
    int main()
    {
        int x;
        int y;
        int result = 0;
        char operation;
        printf("Enter the first number: ");
        scanf("%i", &x);
        printf("Enter the second number: ");
        scanf("%i", &y);
        printf("Choose an operator\n");
        printf("1=add, 2=sub, 3=mult, 4=div\n");
        scanf("%i", &operation);
        switch(operation)
        {
        case 1:
            result = x+y;
            break;
    
    
        case 2:
            result = x-y;
            break;
    
    
        case 3:
            result = x*y;
            break;
    
    
        case 4:
            result = x/y;
            break;
        }
        printf("Your result is %i", result);
        getch();
    
    
        return 0;
    }

    No errors, no warnings
    simple calculator: what's wrong with this code?-1ekgvue-png

  8. #8
    Registered User
    Join Date
    Apr 2014
    Posts
    12
    Quote Originally Posted by Owais View Post
    Don't go in too deep with %i, just use %d.
    Tried. Still gives me the output of x instead of result

  9. #9
    Registered User
    Join Date
    Nov 2010
    Location
    Long Beach, CA
    Posts
    5,907
    Compile at maximum warning level, you should see something like the following:
    Code:
    $ make foo
    gcc -Wall -ggdb3 -pedantic -std=gnu99 -O0 -o foo foo.c -lm -lpthread -lrt
    foo.c: In function ‘main’:
    foo.c:16:5: warning: format ‘%i’ expects argument of type ‘int *’, but argument 2 has type ‘char *’ [-Wformat]
    foo.c:36:5: warning: implicit declaration of function ‘getch’ [-Wimplicit-function-declaration]
    /tmp/ccMa7s5g.o: In function `main':
    /usr/local/google/home/cagarvin/sandbox/cprogramming/foo.c:36: undefined reference to `getch'
    collect2: ld returned 1 exit status
    You must use the correct scanf format specifier for the type you are reading into. As you have been told before, use " %c" (note the space) for reading in operation.\

    Second, you need to realize that '1' and 1 are different. '1' is a character, for example, read by %c with scanf. 1 is a number, read with %d or %i for scanf. Decide whether you want operation to be a char or an int. Then, make sure you declare it of the right type, use the right format specifier for scanf, and use the correct value in your case statement:
    Code:
    case '1': // if operation is a char -- note the ' ' single quotes
    // or
    case 1:  // if operation is an int
    [EDIT]
    Ultimately, you should learn to use a debugger so you can trace code line by line and examine all relevant values. Pending that, at least get in the habit of using printf statements to print important values at critical points in your program. If you printed operation with "%i", you would likely see it has a value like 48, instead of the expected 1, which tells you you're reading it wrong instead of it being calculated incorrectly. In fact, it was never calculated since you didn't hit any of the switch statements -- like all uninitialized automatic variables, it has an arbitrary garbage value.

    You should get in the habit of always putting a default: case in your switch statements to catch cases like this. Have it print/log an error message to help you debug.

    Also, I should point out that on my system, it gave 0 on one run, even though x was 5. Making incorrect/overly specific assumptions like "it gives the value of x" can make it more difficult to determine what is actually happening. You get stuck trying to figure out how it gets the value of x. Start with a less specific assumption like "result has the incorrect value". Then, work on determining where that incorrect value came from: unassigned variable, copied value of x, garbage value from elsewhere (e.g. buffer overflow), etc.
    [/EDIT]
    Last edited by anduril462; 05-27-2014 at 04:39 PM.

  10. #10
    Codus Conjectus spongefreddie's Avatar
    Join Date
    Sep 2010
    Location
    USA
    Posts
    86
    Quote Originally Posted by zer0_r00t View Post
    Edit:
    Code:
    /* A simple program in which the user picks 2 numbers and does mathematical operation ( +, -, * or / )  */
    
    
    #include <stdio.h>
    #include <stdlib.h>
    
    <SNIP>

    No errors, no warnings
    simple calculator: what's wrong with this code?-1ekgvue-png
    Here's how I made it work in code::blocks:

    Code:
    /* A simple program in which the user picks 2 numbers and does mathematical operation ( +, -, * or / )  */
    
    #include <stdio.h>      //this is all you need for your code, getchar is included
    
    int main(void)
    {
        int x, y;
        float a, b;
        int result = 0;
        float divresult = 0.00;                  //just a habit of mine
        int operation;
        printf("Enter the first number: ");
        scanf("%d", &x);                         //using recommended %d instead of %i
        printf("Enter the second number: ");
        scanf("%d", &y);
        printf("Choose an operator\n");
        printf("1 = add, 2 = subtract, 3 = multiply, 4 = divide\n");  //more attractive to user
        scanf("%d", &operation);                                      //float is only needed for result, not integer input
        switch(operation)
        {
        case 1:
            result = x+y;
            printf("Your result is %d", result);    //seemed simpler to include result line
            break;                                  //in every case instead of trying to
                                                    //trying to sort it out outside of switch
        case 2:
            result = x-y;
            printf("Your result is %d", result);
            break;
    
        case 3:
            result = x*y;
            printf("Your result is %d", result);
            break;
    
        case 4:
            a = (float) x;     //recasting results to float for division
            b = (float) y;     //recasting results to float for division
            divresult = a/b;
            printf("Your result is %f", divresult);
            break;
    
        default:
            printf("You made a boo-boo. Run program again.");
        }
        getchar();              //I assume you wished to pause console program before exit
        return 0;
    }
    V8 Interceptor: KDE Neon 5.15
    Steering wheel: gcc 7.3.0 in Code::Blocks 16.01
    Supercharger: NASM 2.13.02
    Engine: AMD Ryzen 7 1700
    Dashboard: NVIDIA GeForce GTX 1060 6GB
    Rusty old trailer for hauling 50% of my Steam games: Windows 7 Pro 64bit SP1
    Roach-infested ORV for Bandlab Sonar: Windows 7 Pro 64bit SP1

  11. #11
    Codus Conjectus spongefreddie's Avatar
    Join Date
    Sep 2010
    Location
    USA
    Posts
    86
    Quote Originally Posted by zer0_r00t View Post
    Edit:
    Code:
    /* A simple program in which the user picks 2 numbers and does mathematical operation ( +, -, * or / )  */
    
    
    #include <stdio.h>
    #include <stdlib.h>
    
    <SNIP>

    No errors, no warnings
    simple calculator: what's wrong with this code?-1ekgvue-png
    Here's how I made it work in code::blocks:

    Code:
    /* A simple program in which the user picks 2 numbers and does mathematical operation ( +, -, * or / )  */
    
    #include <stdio.h>      //this is all you need for your code, getchar is included
    
    int main(void)
    {
        int x, y;
        float a, b;
        int result = 0;
        float divresult = 0.00;                  //0.00 just a habit of mine
        int operation;
        printf("Enter the first number: ");
        scanf("%d", &x);                         //using recommended %d instead of %i
        printf("Enter the second number: ");
        scanf("%d", &y);
        printf("Choose an operator\n");
        printf("1 = add, 2 = subtract, 3 = multiply, 4 = divide\n");  //more attractive to user
        scanf("%d", &operation);                                      //float is only needed for result, not integer input
        switch(operation)
        {
        case 1:
            result = x+y;
            printf("Your result is %d", result);    //seemed simpler to include result line
            break;                                  //in every case instead of trying to
                                                    //manage it outside of switch
        case 2:
            result = x-y;
            printf("Your result is %d", result);
            break;
    
        case 3:
            result = x*y;
            printf("Your result is %d", result);
            break;
    
        case 4:
            a = (float) x;     //recasting input to float for division
            b = (float) y;     //recasting input to float for division
            divresult = a/b;
            printf("Your result is %f", divresult);
            break;
    
        default:
            printf("You made a boo-boo. Run program again.");    //why not?
        }
        getchar();              //I assume you wished to pause console program before exit
        return 0;
    }
    Last edited by spongefreddie; 05-30-2014 at 02:09 AM.
    V8 Interceptor: KDE Neon 5.15
    Steering wheel: gcc 7.3.0 in Code::Blocks 16.01
    Supercharger: NASM 2.13.02
    Engine: AMD Ryzen 7 1700
    Dashboard: NVIDIA GeForce GTX 1060 6GB
    Rusty old trailer for hauling 50% of my Steam games: Windows 7 Pro 64bit SP1
    Roach-infested ORV for Bandlab Sonar: Windows 7 Pro 64bit SP1

  12. #12
    Codus Conjectus spongefreddie's Avatar
    Join Date
    Sep 2010
    Location
    USA
    Posts
    86
    Sorry about the dual replies; I attempted to edit my post and the server stopped responding. When the server's flatulence was finished, I was rewarded with two permanent posts, and an inabilty to delete #10. The only difference between the two is in the edited comments in the code, not the code itself.

    Cheers.
    V8 Interceptor: KDE Neon 5.15
    Steering wheel: gcc 7.3.0 in Code::Blocks 16.01
    Supercharger: NASM 2.13.02
    Engine: AMD Ryzen 7 1700
    Dashboard: NVIDIA GeForce GTX 1060 6GB
    Rusty old trailer for hauling 50% of my Steam games: Windows 7 Pro 64bit SP1
    Roach-infested ORV for Bandlab Sonar: Windows 7 Pro 64bit SP1

  13. #13
    Registered User
    Join Date
    Oct 2006
    Posts
    3,445
    spongefreddie: Do not hand out complete solutions! It is against the forum rules, and is just generally considered bad form, because the OP learns nothing from it.
    What can this strange device be?
    When I touch it, it gives forth a sound
    It's got wires that vibrate and give music
    What can this thing be that I found?

  14. #14
    Registered User
    Join Date
    Apr 2014
    Posts
    12
    Quote Originally Posted by spongefreddie View Post
    Here's how I made it work in code::blocks:

    Code:
    /* A simple program in which the user picks 2 numbers and does mathematical operation ( +, -, * or / )  */
    
    #include <stdio.h>      //this is all you need for your code, getchar is included
    
    int main(void)
    {
        int x, y;
        float a, b;
        int result = 0;
        float divresult = 0.00;                  //just a habit of mine
        int operation;
        printf("Enter the first number: ");
        scanf("%d", &x);                         //using recommended %d instead of %i
        printf("Enter the second number: ");
        scanf("%d", &y);
        printf("Choose an operator\n");
        printf("1 = add, 2 = subtract, 3 = multiply, 4 = divide\n");  //more attractive to user
        scanf("%d", &operation);                                      //float is only needed for result, not integer input
        switch(operation)
        {
        case 1:
            result = x+y;
            printf("Your result is %d", result);    //seemed simpler to include result line
            break;                                  //in every case instead of trying to
                                                    //trying to sort it out outside of switch
        case 2:
            result = x-y;
            printf("Your result is %d", result);
            break;
    
        case 3:
            result = x*y;
            printf("Your result is %d", result);
            break;
    
        case 4:
            a = (float) x;     //recasting results to float for division
            b = (float) y;     //recasting results to float for division
            divresult = a/b;
            printf("Your result is %f", divresult);
            break;
    
        default:
            printf("You made a boo-boo. Run program again.");
        }
        getchar();              //I assume you wished to pause console program before exit
        return 0;
    }

    omg thank you so much!

  15. #15
    Codus Conjectus spongefreddie's Avatar
    Join Date
    Sep 2010
    Location
    USA
    Posts
    86
    Quote Originally Posted by Elkvis View Post
    spongefreddie: Do not hand out complete solutions! It is against the forum rules, and is just generally considered bad form, because the OP learns nothing from it.
    I apologize. Believe it or not, I was ignorant of that rule. It won't happen again.

    I mistakenly thought that the comments I included would be instructive, as they explained the reasons for my alterations to produce a working program.

    I am moved to comment that when I was first learning C, the cprogramming.com forum was a invaluable resource, because I always received answers to my questions. As I recall, no one ever provided the source for an entire program, but then again, the parts they did provide were the only parts I was coding incorrectly.

    I will endeavor to be more instructive and less demonstrative in the future, if I post another response.
    V8 Interceptor: KDE Neon 5.15
    Steering wheel: gcc 7.3.0 in Code::Blocks 16.01
    Supercharger: NASM 2.13.02
    Engine: AMD Ryzen 7 1700
    Dashboard: NVIDIA GeForce GTX 1060 6GB
    Rusty old trailer for hauling 50% of my Steam games: Windows 7 Pro 64bit SP1
    Roach-infested ORV for Bandlab Sonar: Windows 7 Pro 64bit SP1

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. What's wrong with the code(Calculator program)
    By rizwan in forum C Programming
    Replies: 10
    Last Post: 10-19-2011, 05:59 PM
  2. What's wrong with my simple C code?
    By godmoney in forum C Programming
    Replies: 20
    Last Post: 01-03-2011, 10:19 AM
  3. what is wrong in this simple code
    By vikingcarioca in forum C Programming
    Replies: 4
    Last Post: 04-23-2009, 07:10 AM
  4. Simple calculator -- code review
    By jafet in forum C++ Programming
    Replies: 7
    Last Post: 09-22-2006, 11:49 PM
  5. Simple Code Gone Wrong
    By mrlucky0 in forum C Programming
    Replies: 11
    Last Post: 06-20-2003, 07:47 AM