C Programming: Question about repeats

[ElectroNewby]

Hello folks. This is not a micrcontroller but since you guys know C I wanted to ask for your help here... I made a little program (my first one) and it serves well it's purpose. The problem is that when it gives the result, as soon as we hit a key on the keyboard, it exits.
I'd rather have it repeating it's main function.
Thank you very much for any help

 

[3v0]

To get it to repeat use a while(1) loop

int main(int argc, char *argv[])
{
   int choix;
   double Bpm, Result;

   // List of calculation choices
   printf(" 1. blablabla\n");
   printf(" 2. blablabla\n");
   printf(" 3. blablabla\n");

   while(1)
   {
      printf("Option #");  
      scanf("%d", &choix);          
      printf("Enter the ", choix);

      switch (choix)
      {
         case 1:
            printf("Bpm: ");
            scanf("%lf", &Bpm);
            Result = 1+Bpm;
            printf("1 + bpm = %.lf",Result);
            break;
         case 2:
            printf("Bpm: ");
            scanf("%lf", &Bpm);
            Result = 2+Bpm;
            printf("2 + bpm = %.lf",Result);
            break;
         case 3:
            printf("Bpm: ");
            scanf("%lf", &Bpm);
            Result = 3+Bpm;
            printf("3 + bpm = %.lf",Result);
            break;
         default:  // If the user enters an invalide option, the following message will show up:
            printf("The option you selected is not valid. This program will end because I don't know how to loop it \n");
      }  // end case
      getch();
      return 0;
   } // end while(1)
}

I did not fix other errors. Walk through the program like you were the computer, write down the value of each variable as it changes.

Have fun

 

[ElectroNewby]

Hey thank you for the tip, however I can't get it to work. It keeps shutting down after giving the result (when we hit a key)
I corrected my structure a bit tho, thanks for the model, it's a lot more readable (the program is 240 lines).

I'm having fun but I'm a super beginner noob

 

[Rusttree]

I'm sure 3v0 meant to put the "return 0" below the while-loop. If you copied his example directly, that's what's causing the program to exit.

 

[ElectroNewby]

Yeah thank you, now it works !
Only thing is that if I enter, say "a", the error message starts looping to infinity lol

 

[BrownOut]

Try this

while(1)

while(choiceix<1 && choiceix>3) {
...scanf("%d", &choiceix)
}

...

switch(choiceix)....

etc.

 

[ElectroNewby]

doesn't work :|

 

[ElectroNewby]

double-post.

 

[Rusttree]

Looks like 3v0 put a "default" case in his example code to catch an invalid value. He just forgot to put "return 0;" in there to exit out after the error message prints.

 

[ElectroNewby]

Sorry I can't get it to work...

Can you compile this and correct me please ?
I got it to loop but when I enter an alphabetic value it keeps repeating till infinity

I'd just want to correct that...

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

int main(int argc, char *argv[])
{
   int choix;
   double Rpm, Result;

   // Presentation
   printf("This program will **** (censored)\n\n");

   // List of calculation choices
   printf(" 1. Hello             2. Blablabla              3. Third\n");
   printf(" 4. Another blabla\n\n");

   while(1)
   {
     printf("Option #");
     scanf("%d", &choix); 
     printf("Enter the ", choix);


     switch (choix) // choix awaits for a scanned number from the input (keyboard) at ("%d", &choix)
     {  
        case 1:
           printf("Rpm: ");
           scanf("%lf", &Rpm);
           Result = 360000/Rpm;
           printf("The value is = %.lf dollars.\n\n",Result);
           break;
        case 2:
           printf("Rpm: ");
           scanf("%lf", &Rpm);
           Result = 240000/Rpm;
           printf("A whole %.lf peanuts.\n\n",Result);
           break;
        case 3:
           printf("Rpm: ");
           scanf("%lf", &Rpm);
           Result = 160000/Rpm;
           printf("Aaaaaaaaaaaaa = %.lf turds.\n\n",Result);
           break;
        case 4:
           printf("Rpm: ");
           scanf("%lf", &Rpm);
           Result = 180000/Rpm;
           printf("Numer 4 mofo = %.lf .\n\n",Result);
           break;
        
        default: // If the user enters an invalide option, the following message will show up:
           printf("number, from 1 to 4, corresponding to what you want to know. The number you entered was not valid.\n\n");
     } // End case
   } // End while(1)
   getch();
   return 0;
}

 

[Rusttree]

Huh, yeah, all kinds of crazy happens when you type in a non-number value for that scanf. I don't know enough about the inner workings of scanf understand what's happening, but clearly it's having a very difficult time converting a letter into an int.

I played around a little and found that if you use %c instead of %d, it'll convert it into the ASCII character value. You have to drop off the upper byte for some reason, but that can be done easily with a mask. Consulting an ASCII table, you can convert an ASCII value to a numerical value by subtracting 48.

So try this:

while(1)
{
    printf("Option #");
    scanf("%c", &choix);
    choix = choix & 0x00FF;   //mask off the upper byte
    choix = choix - 48;  //subtract 48 to convert from ASCII code to numerical value
    printf("Enter the ");

    switch(choix)
    {
    ....

I'd be happy to elaborate if you need more explanation.

 

[Rusttree]

Just realized I'm being stupid. There's that extra byte appearing because choix is an int type. Using the %c indicates a char type. So if you cast choix as a char, you don't need to use the mask:

int main(int argc, char *argv[])
{
    char choix;
    ......
    while(1)
    {
        printf("Option #");
        scanf("%c", &choix);
        choix = choix - 48;  //subtract 48 to convert from ASCII code to numerical value
        printf("Enter the ");
 
        switch(choix)
        {
        ....