C程序：简单的数学程序

Question

Want to print for example Grade: 4/5 80 percent Program ask a user how many math problems they want to solve and prints out the number of "wrongs/the number of rights" and their grade. I think I dont have my math right at the end of the code cause its printing out for example: Grade: 4/5 -7446528 percent

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# include <stdio.h>

int main()
{
    int NumberOfTimes, AddAns, SubAns, AddCorrect=0, SubCorrect=0, CorrectAnsAdd, CorrectAnsSub, TotalCorrect, TotalWrong, Add;
    int i,a,b,c,d,e,f,g;
    float percent;

    printf("\n");
    printf("-------------------MATH QUIZ------------------------\n");
    printf("Enter the number of Math problems you want to solve:"); //enters the # of problems the program produces
    scanf("%d", &NumberOfTimes);
    printf("\n");
    srand(time(NULL));
    //Random number generator
    for (i=0;i<NumberOfTimes;++i)
    {
        b = rand() %3 + 1;
        c = rand() %3 + 1;
        a = rand() %2 + 1;

        //Random addition problems
        if (a == 1)
        {
            printf("%d + %d = ", b,c);
            scanf("%d", &AddAns);
            d = b + c;
            if (AddAns == d)
            {
                printf("  +Correct\n");
                AddCorrect = AddCorrect + 1;
            }
            //Random subtraction problems
            else
            {
                printf("  +Wrong, it was %d\n", d);
                AddIncorrect = AddIncorrect + 1;
            }
        }
        if (a == 2)
        {
            printf("%d - %d = ", b,c);
            scanf("%d", &SubAns);
            g = b - c;
            //Produces right or wrong answers
            if (SubAns == g)
            {
               printf("  +Correct\n");
               SubCorrect = SubCorrect + 1;
            }
            else
            {
                printf("  +Wrong, it was %d\n", g);
                SubIncorrect = SubIncorrect + 1;
            }
        }
    }
    //Producing the output to wrong/right numbers and grade percentage 
    TotalCorrect = AddCorrect + SubCorrect;
    printf("\n");
    printf("Grade: %d/%d\n",TotalCorrect,NumberOfTimes);
    printf("\n");
    percent=NumberOfTimes/TotalCorrect;
    printf("%d percent \n", percent);
    return 0;
}

Answer 1

There are a few things going on. First, to print a float with printf , use %f . %d is for int s.

Secondly, when you calculate percent , you're accidentally using integer division. Since NumberOfTimes and TotalCorrect are both integers, NumberOfTimes/TotalCorrect performs integer division and produces an int . It's only converted to a float after the whole initializing expression is evaluated. Use this instead:

percent = (float)TotalCorrect / NumberOfTimes;
// OR, if you want an actual percent:
percent = 100.0f*TotalCorrect/NumberOfTimes;

Then, using %f :

printf("%f percent\n", percent); // "80.000000 percent"

Note that this will display the percentage out to many decimal places; if you want a cleaner display without a decimal point, you could just calculate the percent as an int :

// multiply before dividing to avoid integer division problems
int percent = 100*TotalCorrect/NumberOfTimes;
printf("%d percent\n", percent); // "80 percent"

Hope this helps!

Answer 2

In C, dividing two integers won't get you a floating point number, even if the assignment is to a float. It's just how the language works. You'll have to cast NumberOfTimes and TotalCorrect as floats.

So replace percent=NumberOfTimes/TotalCorrect; with

percent=(float)TotalCorrect/(float)NumberOfTimes * 100;

Furthermore, you're trying to print a float as an integer in the line

printf("%d percent \n", percent);

which is giving you a wonky result. Instead, try:

printf("%d percent \n", (int)percent);