Thread: Guidance - Grading Issues/variable problem

Ugh...I'm probably pulling up threads from the grave here, but I've read the ones that deal with sort of this issue, however it's setup differently than what I'm currently doing.

I'm stumped and need a bit of guidance on this particular code.

I've built everything out, however I'm trying to figure out how to collect the data for my "validGrades" variable.

Is there a way to collect the data from the "else" and have it dump it's information into the "validGrades"?

As you can see from my code, I have it commented out, along with my equation/formula below. The only thing missing is my "validGrades" that I just can't figure out how to implement.

My lack of knowledge in this is preventing me from moving forward. Can anyone drop some knowledge bombs on me?
Sorry, I'm completely new to this.

Thanks!

Code:

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

main(){


    //variables
    int score;
    int passingGrades = 0;
    int percentagePassing = 0;
    int validGrades = 0;


    //getting data from the user
    printf("Enter a test score (-1 to quit): \n");
    scanf_s("%i", &score);


    //while loop
    while (score != -1){
        if (score > 100 || score < 0){
            printf("This is NOT a valid grade. \n");
            printf("Please enter a valid grade. \n");
        } else {
            passingGrades = passingGrades + (score >= 70);
            //validGrades = 
            printf("Is a valid grade. \n");
            printf("Number of valid grades: %i \n", validGrades);
            printf("Number of passing grades: %i \n", passingGrades);
        }
        printf("Enter a test score (-1 to quit): \n");
        scanf_s("%i", &score);
    }


    //output results
    printf("The number of passing grades is: %i \n", passingGrades);


    //percentagePassing = (passingGrades / validGrades) * 100;
    printf("%i%% of the valid grades entered are passing grades. \n", percentagePassing);


    //bring up console window
    system("pause");


}

i think in the else part you should check if score is greater than equal to 70, in that if loop you should add score with passing grade as passinGrades = passingGrades + score and increment validGrades as validGrades+1.

ok I would say your percentage formula is backwards! (follows the solving of cross multiply)
passing grades X
---------------- = ---
valid grades 100

either way, you need to put a check in there, to make sure your not dividing by 0! it will crash your program!


Satya

if you check score the way you say, it would add score to the passingGrade!

in her current code with the if, (score >= 70) returns 1 if true, and 0 if not, so the code is fine!

Okay...I'm sort of understanding, especially adding an extra counter in there.
However now it's counting double on the passingGrades as 1...then the next for validGrades is catching the 1 as well, and adding another 1...so creating 2. When there is only 1.

I created this, but yeah, I need to fix the formula...

Code:

main(){


    //variables
    int score;
    int passingGrades = 0;
    int percentagePassing;
    int validGrades = 0;


    //getting data from the user
    printf("Enter a test score (-1 to quit): \n");
    scanf_s("%i", &score);


    //while loop
    while (score != -1){
        if (score > 100 || score < 0){
            printf("This is NOT a valid grade. \n");
            printf("Please enter a valid grade. \n");
        } else {
            passingGrades = passingGrades + (score >= 70);
            validGrades = passingGrades + (score >= 70);
            printf("Is a valid grade. \n");
            printf("Number of valid grades: %i \n", validGrades);
            printf("Number of passing grades: %i \n", passingGrades);
        }
        printf("Enter a test score (-1 to quit): \n");
        scanf_s("%i", &score);
    }


    //output results
    printf("The number of passing grades is: %i \n", passingGrades);


    percentagePassing = (passingGrades / validGrades) * 100;
    printf("%i%% of the valid grades entered are passing grades. \n", percentagePassing);


    //bring up console window
    system("pause");


}

Oops...however I guess this wouldn't work, because I need all valid Grades, 0-100...not just scores of 70.

Uhmm...did I just get this? lol...I feel so dumb as I'm so new to this stuff...

Code:

main(){


	//variables
	int score;
	int passingGrades = 0;
	int percentagePassing;
	int validGrades = 0;


	//getting data from the user
	printf("Enter a test score (-1 to quit): \n");
	scanf_s("%i", &score);


	//while loop
	while (score != -1){
		if (score > 100 || score < 0){
			printf("This is NOT a valid grade. \n");
			printf("Please enter a valid grade. \n");
		} else {
			passingGrades = passingGrades + (score >= 70);
			validGrades = validGrades + (score >= 100);
			printf("Is a valid grade. \n");
			printf("Number of valid grades: %i \n", validGrades);
			printf("Number of passing grades: %i \n", passingGrades);
		}
		printf("Enter a test score (-1 to quit): \n");
		scanf_s("%i", &score);
	}


	//output results
	printf("The number of passing grades is: %i \n", passingGrades);


	percentagePassing = (passingGrades / validGrades) * 100;
	printf("%i%% of the valid grades entered are passing grades. \n", percentagePassing);


	//bring up console window
	system("pause");


}

Why cannot you write validGrades = validGrades + 1;?

Yeah, sorry, it's still having issues.

Also, sorry, it's because if I do a validGrades + 1...won't it read all inputs?
An example is because what I'm following is, validGrades are from 0 - 100.

So if someone types in 123, that shouldn't be valid. Or a -2.

SATYA, you are still a little off!!!

AccipiterZ, that is why I said look into the "Loop Counter for your valid grade count"

in a loop for example

Code:

for(int x = 0;x < 10;x++)

everyloop through the for, x is counted up one (x++)

and because the "counter" would be in your else section, it will only add it once per every valid grade!

Well, I guess with a

Code:

validGrades = validGrades +  1;

It looks like it's counting correctly.
So if I input, example:

45
90
70
87
123
100

It is counting 5 valid grades, and 4 passing grades. Which is correct.

Is that because it's hitting the if statement first?



Now my problem seems to be the formula.

Code:

main(){


    //variables
    int score;
    int passingGrades = 0;
    int percentagePassing = 0;
    int validGrades = 0;


    //getting data from the user
    printf("Enter a test score (-1 to quit): \n");
    scanf_s("%i", &score);


    //while loop
    while (score != -1){
        if (score > 100 || score < 0){
            printf("This is NOT a valid grade. \n");
            printf("Please enter a valid grade. \n");
        } else {
            passingGrades = passingGrades + (score >= 70);
            validGrades = validGrades + 1;
            printf("Is a valid grade. \n");
            printf("Number of valid grades: %i \n", validGrades);
            printf("Number of passing grades: %i \n", passingGrades);
        }
        printf("Enter a test score (-1 to quit): \n");
        scanf_s("%i", &score);
    }


    //output results
    printf("The number of passing grades is: %i \n", passingGrades);


    percentagePassing = (passingGrades / validGrades) * 100;
    printf("%i%% of the valid grades entered are passing grades. \n", percentagePassing);


    //bring up console window
    system("pause");


}

Code:

passingGrades = passingGrades + (score >= 70);

While this line technically accomplishes what you're trying, I'd suggest using an "if" to determine whether "passingGrades" should be incremented - it's just more clear.

In fact, I'd be curious to know if you understand how "passingGrades" is incremented in that snippet.

I had someone else tell me to adjust that as well, with something like...

Code:

passingGrades += (score >= 70);

Which honestly I don't understand the "+" of it and I'll have to look that up.

However, I do understand...

Code:

passingGrades = passingGrades + (score >= 70);

passingGrades is currently set to 0.
When a "score" is typed in by the user, it's checking whether it's greater than or equal to 70.
If it is, it's creating a "1".
As passingGrades is currently set to 0, 0 +1 is now 1.
And so on.

passingGrades is anything 70 and above that is typed in by the user.
passingGrades is now being saved into memory.