how do you make a function return a value?

[panfilero]

I'm trying create a function, but when it returns my value instead of a number I get a combination of letters and numbers.

I input: 0 and 4

I should get something like: 3.313

I get: 1.#QNAN0

Here's my code, do I need to do something different with my return command?

thank you

#include <stdio.h>
#include <math.h>
#include <stdlib.h>


float secant ( float x_lower,float x_upper);


main()
       {
            float root, lower_bound, upper_bound ;       
            
                   
            
            printf("\n\nInput lower bound:  ");
            
            scanf("%d", &lower_bound); 
            
            printf("\n\nInput upper bound:  ");
            
            scanf("%d", &upper_bound); 
            
            root = secant ( lower_bound, upper_bound );
                
              printf("\n\n answer is:  %f ",root);
              
              getchar();
              getchar();
                }
                
                
float secant ( float x_lower,float x_upper) {
      
      int i ;
      float xo, xi ;
      
      for ( i = 1 ; i < 4 ; i++ ) {
          
          
   xo = exp ( -pow (x_lower , 2) ) - cos ( x_lower ) - 1 ;
   
   xi = exp ( -pow (x_upper , 2) ) - cos ( x_upper ) - 1 ;


 x_upper = xi - ( xi/(xo-xi) ) * ( x_lower - x_upper ) ;
 
}

return x_upper ;

}

[kermit]

You might want to make a different variable in your secant function and assign your return values to it...

float secant(float x_lower, float x_upper)
{

        int i;
        float xo, xi;
        float some_var;

        for (i = 1; i < 4; i++) {


                xo = exp(-pow(x_lower, 2)) - cos(x_lower) - 1;

                xi = exp(-pow(x_upper, 2)) - cos(x_upper) - 1;


                some_var = xi - (xi / (xo - xi)) * (x_lower - x_upper);

        }

        return some_var;
}

Also, this nitpick:

scanf("%d", &upper_bound);

Use %f for float input

[panfilero]

Thanks for the tip, I'm still getting letters for my output instead of a number? Do you know why?

[Rashakil Fol]

Your scanf calls are using %d when they should be using %f. With many inputs, this causes the floating point approximation to be filled with bits that represent an "infinite" or "not a number" value. With other inputs, this gives the floating point approximation a completely wrong value.

[Salem]

> Also, this nitpick:
It's not a nitpick, it's fundamentally broken unless it's fixed.

gcc -W -Wall -ansi -pedantic -O2 foo.c -lm
foo.c:10: warning: return type defaults to ‘int’
foo.c: In function ‘main’:
foo.c:17: warning: format ‘%d’ expects type ‘int *’, but argument 2 has type ‘float *’
foo.c:21: warning: format ‘%d’ expects type ‘int *’, but argument 2 has type ‘float *’
foo.c:29: warning: control reaches end of non-void function