Trying to do basic math functions. Why doesn't this work?

This is a discussion on Trying to do basic math functions. Why doesn't this work? within the C Programming forums, part of the General Programming Boards category; Hello, I'm trying to write a simple program that calculates projectile distance and time. I was given the basic equations ...

  1. #1
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    Trying to do basic math functions. Why doesn't this work?

    Hello,
    I'm trying to write a simple program that calculates projectile distance and time. I was given the basic equations but I'm writing something incorrectly because my output is currently zero. I have a feeling this may be an explicit type casting issue but I'm not sure what to do:
    Code:
    #include <stdio.h>
    #include <math.h>
    
    
    int main(void)
    {
       const double PI = 3.14, GRAVITY = 9.8;
       double degrees = 0, velocity = 0, angle = 0, range = 0, time = 0 ;
    	
    	
       printf("Enter the measure of the angle in degrees. \n");  
       scanf("%d", &angle);
    	
       printf("Enter the initial velocity. \n");  
       scanf("%d", &velocity);
    	
       angle = angle * (PI/180.0);
       range = (sin(2 * angle)) * pow(velocity, 2)/ GRAVITY;
       time  = range/(velocity * (cos(angle)));
      	
       printf("The projectile will travel %d meters.\n", range);
       printf("It will take %d seconds.\n", time);
       
       return 0;
    }
    Can anyone offer hints as to how I should fix this?

    Thanks in advance,
    crazychile

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    Do not use &#37;d to read a double.
    I believe the correct is %lf (but check the docs to be sure).
    And don't print doubles using %d; use %f.

    It's YOUR responsibility to tell scanf/printf/etc the correct type you are passing to it (this can be avoided in C++, but not C). If you do not, you will get unexpected results or crashes. Or simply put, undefined behavior.
    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.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

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    To clarify, the program compiles but the output values for the print statements are each zero.
    Thank you,
    crazychile

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    Yes, I'm sure it does, but this is a runtime error, not a compile error.
    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.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

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    ALL HAIL ELYSIA!!!!


    That worked!
    Thanks,
    crazychile

  6. #6
    Kernel hacker
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    Depending on which compiler you are using, enabling warnings may actually tell you that the format for the printf and scanf are wrong. It would be a warning, but it's still a lot more help than trying to figure out yourself what you got wrong.

    --
    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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