Extreme beginner quadratic roots solver

This is a discussion on Extreme beginner quadratic roots solver within the C Programming forums, part of the General Programming Boards category; Right, so I am brand new to programming (doing it for a module at uni). We have to write a ...

  1. #1
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    Extreme beginner quadratic roots solver

    Right, so I am brand new to programming (doing it for a module at uni). We have to write a programme to find real solutions to a quadratic to 3 decimal places. We need to use command line arguments and the if-else construct.

    Looking over various code I have found online and the very little that I actually do understand, I put this together and would like to understand what it all means I have made bold the bits I am unsure about.


    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <math.h>
    
    int main(int argc, char* argv[])
    {
         double  a, b, c, valida, validb, validc, x1, x2;
         int     valid_input;
    	 
         if(argc != 4)								
         {
            printf("Enter three arguments\n");
            exit(EXIT_FAILURE);
         }
    	 
         else
         {
            valida=sscanf(argv[1], "%lg", &a);
            validb=sscanf(argv[2], "%lg", &b);
    	validc=sscanf(argv[3], "%lg", &c);
    
    	valid_input = (valida != 0) && (valida != EOF);
            valid_input = valid_input && (validb !=0) && (validb != EOF);
    	valid_input = valid_input && (validc !=0) && (validc != EOF);
    	
            if(!valid_input)
            {
    			printf("Please enter 3 valid digits...\n");
    			exit(EXIT_FAILURE);
            }
    		
    		else
    		{
    					
    			if((a==0)&&(b==0))
    			{
    				printf("It is not possible to find the roots of these numbers \n");
    				printf("as both 'a' and 'b' coefficients are zero\n");
    				exit(EXIT_FAILURE);
    			}
    			
    			if(a==0)
    			{
    				x1 = (-(c/b));
    				printf("There is 1 root");
    				printf("x1 = %.3lf\n",x1);
    			}
    			
    			else
    			{
    					if(((b*b)-(4*a*c)) > 0)
    					{  
    						x1 = ((-b)+(sqrt((b*b)-(4*a*c))))/(2*a);
    						x2 = ((-b)-(sqrt((b*b)-(4*a*c))))/(2*a);
    					
    						printf("There are 2 roots\n");
    						printf("x1 = %.3lf\n",x1);
    						printf("x2 = %.3lf\n",x2);
    						exit(EXIT_SUCCESS);
    					}
    		
    					if(((b*b)-(4*a*c)) == 0)
    					{
    						x1 = ((-b)/(2*a));
    					
    						printf("There is 1 root\n");
    						printf("x = %.3lf\n",x1);
    						exit(EXIT_SUCCESS);
    					}
    		
    					else
    					{
    						printf("Cannot calculate imaginary roots\n");
    						exit(EXIT_FAILURE);
    					}	
    					
    					
    			}
    		}
    	 }
    	 
    	 
    	 return(0);
    }
    For the first bold bit;
    -Should I be using float or double?
    -Is it right to set valid_input as an integer?
    -Should I define a,b,c,x1,x2 before main()?

    For the second (validation);
    -Is %lg correct? and if using float, it should be %f, right?
    -In the valid_input bit, have I said that it is only valid if ALL 3 lines are met or is each one separate (as in is it only invalid if a,b and c are zero, or if any of them are)?

    For the third bit;
    -Is %.3lf correct for 3 decimal places?
    -Would it be different if it was a float? %.3f?
    -Does it need an exit(EXIT_SUCCESS) after it?

    In general;
    -Should I define the discriminant before main() and then use it in the if-else instead?

    ---------------------------

    I apologise if I have gone against any board rules, I have read the FAQ and searched the forum before posting and tried to follow the guidelines....

    Thanks

  2. #2
    Epy
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    Float should be fine. Int is correct, logical statements return 1 or 0 as signed integers. Define your variables inside of main() like you already have it.

    Should be %.3f for a float, I believe.

    The exit() function is more for when errors are encountered, as I understand it. Should use return instead.

  3. #3
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    The sscanf() parts you highlighted are used to just locate and put the right values from the *argv[] (a 2 D array), into the correct variables: a, b, or c

    sscanf() is scanf() used on a designated string.

    .3lf is the printf() format for a double, printed out to 3 decimal places.

  4. #4
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    Thanks, so

    valida=sscanf(argv[1], "%f", &a)

    would assign the first command line argument to the variable a in the programme....

    but what about thei valida? is that another variable I have created? or does that mean something like, "to validate a the assignment of it must be a float?

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