checking if entered a char
 

hello!
Well I must write a program that recieves 3 arguments and then returns if those 3 arguments make for a triangle (Equilateral triangle, Isosceles triangle and Scalene).
For such the program must recieve only integers but we have to use this sentence:

const char* Triang(int argc, char *argv[]) { ... }

so the user can enter text as the second argument... The idea behind is that we learn how to differ from a char/string and an integer...
however i do not know how to accomplish this...
I know how to find out which type of triangle it is but not how to know if the user entered a letter or a string (say 'apple', '/', etc).
Thanks for the time =D

/* returns 0 if not integer 1 if integer */
int is_input_integer(char *input) {
while (*input) {
if (!isdigit(*input++))
return 0;
}
return 1;
}


call it like
is_input_integer(argv[i])

or you could use this:

int a, b, c, d, e, f;
if (1 == sscanf (argv[1], "%d", &a))
/*first number was an int*/;
if (1 == sscanf (argv[2], "%d", &b))
/*second too*/
if (1 == sscanf (argv[3], "%d", &c))
...
...
if (1 == sscanf (argv[6], "%d", &f))
/*Houston, we have a triangle*/

a `cleaner' design would be to use a struct point { int x, y; };

Hope this helps,

Jonas Kölker

Thank you both very much!!
your help has been of great use! :D