Thread: Validating Numbers only

Hey Guys,

I'm new to the C language.

I'm trying to validate numbers only when you take input from the user. I don't want to accept alpha characters in there. But i can't figure it out. Here's my code.

/*Currency Conversion Program*/

#include<stdio.h>
#include<ctype.h>
main()
{
/*intergers declared*/
float pesos = 11.3896, canadad = 1.18503, dem = 1.49923;
float francs = 5.02760, aud = 1.27688;
float america, mexico, canada, germany, france, australia;
char dummy;

/*requests input from user*/
printf("\nCurrency Conversion\n");
printf("\nPlease Enter US Dollars to be Converted: $");
scanf(" %f", &america);

/*loops statements if condition is met*/
while(america<= 0)
{
printf("\nPlease insert a valid number entry > 0: $");
scanf(" %f", &america);
}

/*Hard Coded Equations*/
mexico = america * pesos;
canada = america * canadad;
germany = america * dem;
france = america * francs;
australia = america * aud;

/*US Dollars Displayed and Converted According to Country*/
printf("\n-----------------------------\n");
printf("US Dollars Entered: $%.2f\n", america);
printf("-----------------------------\n");
printf("\nConverted Currency by Country:\n\n");
printf("Mexico's Pesos: %.2f\n", mexico);
printf("Canada's Dollars: %.2f\n", canada);
printf("Germany's Marks: %.2f\n", germany);
printf("France's Francs: %.2f\n", france);
printf("Australia's Dollars: %.2f\n", australia);

/*Requests user to end program*/
printf("\nPress enter to exit: ");
scanf("%c", dummy);

return 0;

}

Please use [code][/code]Tags

sorry about that guys. Please help me figure out how to accept numbers only.

Code:

/*Currency Conversion Program*/

#include<stdio.h>
#include<ctype.h>
main()
{
   /*intergers declared*/
   float pesos = 11.3896, canadad = 1.18503, dem = 1.49923;
   float francs = 5.02760, aud = 1.27688;
   float america, mexico, canada, germany, france, australia;
   char dummy;

   /*requests input from user*/
   printf("\nCurrency Conversion\n");
   printf("\nPlease Enter US Dollars to be Converted: $");
   scanf(" %f", &america);

   /*loops statements if condition is met*/ 
   while(america<= 0)
   {
       printf("\nPlease insert a valid number entry > 0: $");
       scanf(" %f", &america); 
   }

   /*Hard Coded Equations*/
   mexico = america * pesos;
   canada = america * canadad;
   germany = america * dem;
   france = america * francs;
   australia = america * aud;

   /*US Dollars Displayed and Converted According to Country*/
   printf("\n-----------------------------\n");
   printf("US Dollars Entered: $%.2f\n", america);
   printf("-----------------------------\n");
   printf("\nConverted Currency by Country:\n\n");
   printf("Mexico's Pesos:      %.2f\n", mexico);
   printf("Canada's Dollars:    %.2f\n", canada);
   printf("Germany's Marks:     %.2f\n", germany);
   printf("France's Francs:     %.2f\n", france);
   printf("Australia's Dollars: %.2f\n", australia);

   /*Requests user to end program*/
   printf("\nPress enter to exit: ");
   scanf("%c", dummy);

   return 0;

}

I'm not going to give you code, but I'll give you advice:

Try looking in to the isdigit function and get the input as a string instead of a number. This way you can check to see if there are any invalid letters in there (don't forget that a . is a valid letter in a floating-point number!!)

does that means using getchar() instead of scanf()? also how would i convert the string number back into a float variable?

whenever you take in input from the user,check for ascii values other than those of the digits and dots that you want to accept.if the ascii values are not the same as the ones for the digits,print an error else continue.
ciao

I knew somebody was going to say that. I read that FAQ, and I've read about it elsewhere. I use Visual C++ 2003. If you look at MSDN 'fflush' works fine with 'stdin'. If you use a different compiler, you need to look at the documentation for your compiler as 'fflush(stdin)' is an extension to standard C.

What do you all think about using 'rewind(stdin)' to clear the keyboard buffer? Visual C supports it.