Thread: While loop in menu help!!

Code:

I AM HAVING PROBLEMS WITH THE MENU. AFTER TYPING IN A CASE OPTION THE MAIN MENU SHOULD RE-APPEAR BUT DOES NOT.
ANY SUGGESTIONS

#include <stdio.h>
#include <math.h>
#include <grx20.h>


#define length 2

 int n, i, menu1;
 float m, y, y0, x, y, x1[length], y1[length], xsum, ysum, xysum, xsq[length]; 
 float xsqsum, b[length], xres, yres, xplot, xploti, yplot, yploti, y2[length];


main()

{          
      
      /* Main menu */
     
      menu1 = 1;
      while (menu1==1)
          
      {
          n = length;     
          xsum = 0;
          ysum = 0;
          xysum = 0;
          xsqsum = 0;
           
          printf("What do you want to do?   Select an option\n\n");
          printf("1. Input data\n");
          printf("2. View table of data\n");
          printf("3. Plot line of best fit\n");
          printf("4. Exit program\n");
          scanf("%d", &menu1);
      
          switch (menu1)
          {
                 case 1:
                      
                      /* Generate set of data */                   
     
                      printf("\nEnter the number of x-y values: ");     
                      scanf("%d", &n);                         
                        
                      for (i=0; i<n; i++ )                                          
                      {
                          printf("Enter x-y values separated by a space: ");
                          scanf("%f %f", &x, &y);
                    
                          x1[i] = x;
                          xsq[i] = x1[i]* x1[i];
                          y1[i] = y;
                          xsum = xsum + x1[i];
                          xsqsum = xsqsum + xsq[i];
                          ysum = ysum + y1[i];
                          xysum = xysum + (x1[i]*y1[i]);
                          
                      }
                           
                      /* Calculate gradient */
                      m = ((n * xysum) - (xsum * ysum)) / (n * (xsqsum)) - 
                      (xsum * xsum);
                    
                      /* Calculate y-intercept */
                      y0 = (ysum - (m * xsum)) / n;
                 
                      for (i=0; i<n; i++ )
                      {
                         
                          y2[i] = y0 + m*x1[i];
                          b[i] = y2[i] - y1[i];
                         
                      }      
                    
                      printf("Gradient = %f, y-intercept = %f\n", m, y0);
                      scanf("%d", &i);
                      break;
                      
                    
                      case 2:
                           printf("X \t Y \t y-Y");
                           for (i=0; i<n; i++ )
                           {
                                                                                                                                           
                               printf("%f %f %f", x1[i], y1[i], b[i]);
                           }
                           scanf("%d", &i);
                           break;
               
                      case 3:
                           for (i=1; i<n; i++ )
                           {
                                                                                      
                               GrColor bgColour = 0;        /* background colour*/
                               GrColor pColour = 2;         /*plot colour*/
               
                               GrSetMode(GR_default_graphics);
                               xres = GrScreenX();
                               yres = GrScreenY();
                         
                               /*GrClearScreen(bgColour);*/
                         
                               xplot = x1[i-1];
                               xploti = x1[i];
                               yplot =  y1[i-1];
                               yploti = y1[i];
                               GrLine(xplot, yplot, xploti, yploti, pColour);
                      
                      
                           }
                           system ("PAUSE");
                           GrSetMode(GR_default_text);
                           break;
               
                           case 4: 
                                menu1 = 0;
                                            
                           default:
                                   printf("Invalid option. Try again\n");
                                   system ("PAUSE");
               }
      }       
}

More to your point, menu1 only stays equal to 1 the first time through, or if the user's menu choice is also 1. Once you choose something else (like 2 or 3, etc.) in the menu, menu1 changes and the while kicks out.

Try ... while (menu1 != 4)

His final case, 4, sets menu1 = 0 so he should test for menu1 != 0.

I say this because if, in the future, he adds another menu item (and its necessary case statement) he doesn't have to edit the while()

Originally Posted by mike65535

His final case, 4, sets menu1 = 0 so he should test for menu1 != 0.

I say this because if, in the future, he adds another menu item (and its necessary case statement) he doesn't have to edit the while()

Good catch... I looked at the menu and saw option 4, but didn't check the cases... my bad.