Thread: first program has me stumped

hey, this is my first c program (yeah, helloworld wasn't challenging enough). But it gets down to a linking error... could anyone let me know what I am doing wrong?

Code:

#include <stdio.h>
 
int main()
{
   float rt=0;
   float y=0;
   float yt=0;
   float p=0;
   float r=0;
   float t=0;
   char s[10];
   float i=0;
   
    printf("How much money will you pay per week?\n");
    gets(s);
    p=atoi(s);
    printf("What is the interest rate?\n");
    gets(s);
    r=atoi(s);
    printf("How many years will you make payments?\n");
    gets(s);
    yt=atoi(s);
    yt=yt+1;
    for(y=0;y<yt;y++)
    {
                     i=((p*52)+t)*r;
                     printf("You will make %.2d in interest in %d years.\n",i,y);
                     rt=i=(p*52);
                     t=t+rt;
                     printf("You will make %.2d total in %d years.\n",t,y);
                     printf("Press Enter.\n");
                     getchar();
    }
                     return(0);
}

could anyone let me know what I am doing wrong?

O_o

Well, the first thing that I noticed that you are doing wrong is not posting the error messages you got along with your source.

Start by correcting that by posting the errors you are getting.

Soma

Okay, I caught the stdlib.h exclusion, downloaded codeblox, and built the program. It actually ran with codeblox, but it returns 0 every time, and the number of years is returned as a 8 digit number. I don't understand the reference to misusing gets(). I am learning this all on my own, so I'm sorry if this stuff sounds dumb.

How much money will you pay per week?
1
What is the interest rate?
1
How many years will you make payments?
5
You will make 00 in interest in 1078591488 years.
You will make 00 total in 1078591488 years.
Press Enter.
You will make 00 in interest in 1079640064 years.
You will make 00 total in 1079640064 years.
Press Enter.
You will make 00 in interest in 1080262656 years.
You will make 00 total in 1080262656 years.
Press Enter.
You will make 00 in interest in 1080688640 years.
You will make 00 total in 1080688640 years.
Press Enter.
You will make 00 in interest in 1081098240 years.
You will make 00 total in 1081098240 years.
Press Enter.
You will make 00 in interest in 1081311232 years.
You will make 00 total in 1081311232 years.
Press Enter.

Process returned 0 (0x0) execution time : 7.804 s
Press any key to continue.

Code:

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

int main()
{
   float rt=0;
   float y=0;
   float yt=0;
   float p=0;
   float r=0;
   float t=0;
   char s[10];
   float i=0;
   
    printf("How much money will you pay per week?\n");
    gets(s);
    p=atoi(s);
    printf("What is the interest rate?\n");
    gets(s);
    r=atoi(s);
    printf("How many years will you make payments?\n");
    gets(s);
    yt=atoi(s);
    yt=yt+1;
    for(y=0;y<yt;y++)
    {
                     i=((p*52)+t)*r;
                     printf("You will make %.2d in interest in %d years.\n",i,y);
                     rt=i=(p*52);
                     t=t+rt;
                     printf("You will make %.2d total in %d years.\n",t,y);
                     printf("Press Enter.\n");
                     getchar();
    }
                     return(0);
}

Originally Posted by cybalicist

I don't understand the reference to misusing gets().

Why gets() is bad

okay, yeah, I knew about that, but I don't know about the formatting stuff for the alternative yet. I figured this was okay just for testing purposes and practice.

so, changed the %.2d to %.2f, I knew that, but had forgotten, changed the y and yt variables to int's, and it runs fine, but it completely ignores the interest, the i variable...

Code:

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

int main()
{
   float rt=0;
   int y=0;
   int yt=0;
   float p=0;
   float r=0;
   float t=0;
   char s[20];
   float i=0;

    printf("How much money will you pay per week?\n");
    gets(s);
    p=atoi(s);
    printf("What is the interest rate?\n");
    gets(s);
    r=atoi(s);
    printf("How many years will you make payments?\n");
    gets(s);
    yt=atoi(s);
    for(y=0;y<yt;y++)
    {
                     i=(p*52+t)*r;
                     printf("You will make %.2f in interest in %d years.\n",i,y+1);
                     rt=i+(p*52);
                     t=t+rt;
                     printf("You will make %.2f total in %d years.\n",t,y+1);
                     printf("Press Enter.\n");
                     getchar();
    }
    return(0);
}

When I wrote this I planned on using descriptive var names, but it was faster to abbreviate on paper, and I didn't know about this forum, hindsight is 2020. Rt is running total, t is total, y is years, yt is years total, p is payment amount, r is rate of interest, s is placeholder for string input, I is interest accrued. In I=(p*52+t)*r, it means multiply the payment amount times 52, for weeks in a year, add the total, which I assume on the first run would be 0 since I set it at zero earlier, (although I wonder if it's acting as a local var instead of a global), and multiply the result by the rate of interest then store it in I. For rt=I+(p*52) is interest accrued plus the product of the payments for a year goes into rt.

Ok, you might not have know about the forum, fair enough, but you ought to know about your editor, and your editor should have auto-completion to help you type those lenghty variable names. It is critical to use good variable names. Later on you might want to rename a variable and doing a search and replace on variable r is nasty as opposed to search and replace on rate_of_interest.
Also, don't hard codes values like 52. Use #define WEEKPERYEAR 52.