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

int main( int argc, char **argv )
{
    int i,j;
    float a,b;

    if ( argc != 3 ) {
        printf("You need 2 argments.\n");
        return EXIT_FAILURE;
    } 

    for (i=1; i<3; i++) {
        for( j = 0; argv[i][j] != '\0'; j++ ) {
            if ( (isdigit( argv[i][j] ) == 0 ) 
                && (argv[i][j] != '-')
                && (argv[i][j] != '.') ) {
                printf( "Illegal charctar was detected");
                printf(" at %d-th charcter ",j);
                printf(" in arg[%d]=[%s].\n", 
                        i, argv[i]);
                return  EXIT_FAILURE;
            }
        }
    }
    a = atof(argv[1]);
    b = atof(argv[2]);
    printf("%f times %f is %f.\n",a, b, a * b);
    return EXIT_SUCCESS;
}