Simple Math Quiz Program

I wrote a simple command line program to help my daughter practice addition and subtraction.  It compiles under NeXTSTEP 3.3 with some warnings, but works fine.

You can compile it using the command:

cc -Wall -o quiz quiz.m -lNeXT_s -lsys_s

I am posting the code here for any recommendations for improvement.  I could improve it to use the AppKit, but for now I just wanted to do something quick and dirty on the command line.  I am a mechanical engineer, not a programmer, so there's probably a better way of doing this.  But it is a good example of some basic Objective-C code, (pre-Foundation for those who care).

My daughter loves using my NeXT for drawing with WetPaint.  Now she can practice her addition and subtraction too.  So she's becoming a new NeXT fan.   :D


Here's the code:


// This program is to teach basic addition
// and subtraction.

#import <objc/Object.h>
#import <stdio.h>
#import <time.h>

@interface Quiz:Object
{
 int value1, value2, answer, score;
 char operation;
}

-setOperation:(char *)anOp;
-generateExpression;
-displayExpression;
-checkAnswer;
-(int)score;
@end

@implementation Quiz

-setOperation:(char *)anOp
{
 operation = anOp;
 score = 0;
}

-generateExpression
{
 srandom(time(NULL));

 value1 = random() % 10 + 1;
 value2 = random() % 10 + 1;

 // my daughter is not familiar with negative numbers.
 if(operation == '-' && value2>value1) {
   answer = value1;
   value1 = value2;
   value2 = answer;
 }
}

-displayExpression
{
 printf("%i %c %i = ?\n",value1, operation, value2);
}

-checkAnswer
{
 scanf("%i", &answer);
 
 switch(operation) {
 case '+':
   if(answer == value1+value2) {
     printf("Correct!\n");
     score++;
   }
   else { printf("Wrong: %i %c %i = %i\n", value1, operation,
       value2, value1+value2);
   }
   break;
 case '-':
   if(answer == value1-value2) {
     printf("Correct!\n");
     score++;
   }
   else {
    printf("Wrong: %i %c %i = %i\n", value1, operation,
       value2, value1-value2);
   }
   break;
 default:
   printf("Unknown operator.\n");
   break;
 }
}

-(int)score
{
 return score;
}

@end

int main (int argc, char *argv[])
{
 int op, n;

 Quiz *mathQuiz = [[Quiz alloc] init];

 printf("Select an operation.\n");
 printf("[1] For addition.\n");
 printf("[2] For subtraction.\n");

 scanf("%i", &op);

 switch (op) {
   case 1:
     [mathQuiz setOperation: '+'];
     break;
   case 2:
     [mathQuiz setOperation: '-'];
     break;
   default:
     printf("Unknown Operation.\n");
     return 0;
 }

 for(n=1; n<=10; n++) {
   [mathQuiz generateExpression];
   [mathQuiz displayExpression];
   [mathQuiz checkAnswer];
 }
 
 printf("You have answered %i out of %i correctly.\n",[mathQuiz score], n-1);

 [mathQuiz free];
 return 0;
}




Brian Moore