Letter question

[IgorZ]

How to make a program that says enter calculation. If a person enters non-numeric letter to say "That is an invalid operation"

[JosAH]

@IgorZ
Check the isdigit() macro from the ctype.h file. For convenience first read in the entire line and check all the chars in it. Note that this gives you a necessary check that still isn't sufficient.

kind regards,

Jos

[Tassos Souris]

Exactly.. if you must support floating point numbers going through the characters and manually checking with isdigit() is not so *promising*..

See at the function strtod() strtol() in header <stdlib.h>
To read the line use fgets() and not gets() or scanf().

[JosAH]

@Tassos Souris
Lexical analysis is a burden, even if you only want to recognize ints; what if the user types eighty nines in a row? Theoretically it's an int. It won't fit in four or even eight bytes though ...

kind regards,

Jos

[Tassos Souris]

I agree.. personally i use doubles and strtod() when i need to.. strtod()
notifies when an overflow or underflow occurs :)

[IgorZ]

How about when a person enters a letter instantly to delete it? Is that possible?

[Savage]

@IgorZ
ungetc() may help, check this out.

You will ofcourse need to modify the sample a bit ^^