Homework Help

[alecmcraig]

I am currently working on a homework assignment and am trying to create a loop in a menu. In the menu, I need to evaluate the input. If it is not a character, I need it to say, "Invalid Entry, try again" and loop back to the input again. My input needs to be one of the following: D, E, L, or Q. If the entry is not correct, it needs to loop back in order to allow the user to input a correct character.

In the following code, I was trying to just evaluate that the input was a character and not a digit. I am using the switch/case below in the program and would like to catch an input error before the program gets to that part.

	s='\0';
	
	while (isdigit(s)==0){
	
	printf("\n\n\tStore selection menu\n\t---------------------\n\n");//Store Menu Menu
	printf("\tD)  Del Mar\n");
	printf("\tE)  Encinitas\n");
	printf("\tL)  La Jolla\n");
	printf("\tQ)  Quit\n\n");
	printf("\tSelect D, E, L, or Q : ");
	scanf("%c", &s);	
	
	if (isdigit(s)==0)
		break;
	else
		printf("\tInvalid response, try again");
		
	}

I have included the <ctype.h> in the beginning of the program. This is just a portion of the program.

[Salem]

Perhaps isalpha rather than isdigit then.

[alecmcraig]

I tried that and it worked, now I've got to figure out how to get the program to loop back if the user enters a character that is not D, E, L, or Q. I am thinking that I need to use that at the bottom of the switch case under default:, but I can't seem to get a grip on which looping structure to use.

[alecmcraig]

I forgot to add my code, here it is:

while (isalpha(s)==0){//beginning of loop to test whether input is a letter, starts as a number.
		
	printf("\n\n\tStore selection menu\n\t---------------------\n\n");//Store Menu Menu
	printf("\tD)  Del Mar\n");
	printf("\tE)  Encinitas\n");
	printf("\tL)  La Jolla\n");
	printf("\tQ)  Quit\n\n");
	printf("\tSelect D, E, L, or Q : ");
	scanf("%c", &s);	
	
	if( isalpha(s) )
		break;
	else
		printf("\n\tInvalid response, try again");
		//this may be of some importance - != is the same as not equal to in C
	}//end of loop
	
	d=7.25;
	e=7.50;
	l=7.75;
	
	//calculations of Sales Tax
	x=p*d*0.01;//del mar result
	y=p*e*0.01;//encinitas result
	z=p*l*0.01;//la jolla
	
	switch (s) {
	
	case 'd': case 'D':
	printf("\n\tStore Name : Del Mar");
	printf("\n\tTax Rate : %.2f", d);
	printf("%%");
	printf("\n\tPurchase Amount : %.2f", p);
	printf("\n\tTax Amount : %.2f", x);
	printf("\n\tTotal Sale Amount : %.2f", p+x);
	break;
	case 'e': case 'E':
	printf("\n\tStore Name : Encinitas");
	printf("\n\tTax Rate : %.2f", e);
	printf("%%");
	printf("\n\tPurchase Amount : %.2f", p);
	printf("\n\tTax Amount : %.2f", y);
	printf("\n\tTotal Sale Amount : %.2f", p+y);
	break;
	case 'l': case 'L':
	printf("\n\tStore Name : La Jolla");
	printf("\n\tTax Rate : %.2f", l);
	printf("%%");
	printf("\n\tPurchase Amount : %.2f", p);
	printf("\n\tTax Amount : %.2f", z);
	printf("\n\tTotal Sale Amount : %.2f", p+z);
	break;
	case 'q': case 'Q':
	exit (1);
	default:
	printf("Invalid Response, Try Again");
	
	}
}

[alecmcraig]

I scraped the whole thing and started over using ASCII codes for letters and using if statements to evaluate and a do/while loop. Everything worked out fine, my homework should be complete after a few cosmetic alterations.