Switch statement within a do...while loop(values stacking) - c

Question

I am a student and just 4 weeks into programming and I hope I can get help here huehue. So I am making a program where you can translate decimal numbers into octal and binary and vice versa. The program continues to ask the user to choose until they choose letter d to exit the program. The program seems to run fine at first but when I tried to use again the same letter and input values, the output seems to stack from the output from the last time, not overwriting I guess(sorry if my terminologies or grammar is wrong, I am not that good in english)What do I need to change? I can't figur it out huhuhu.
#include<stdio.h>
#include<math.h>
int main(){
int c, k, r=0, e=0, dec=0, o=0, place=1;
long n;
char choice, new, d;
do{
printf("Choices:\na. Decimal to binary and octal\nb. Octal to decimal and binary\nd. Exit.\n\n");
printf("enter your choice:\t");
printf("\n");
scanf(" %c", &choice);
switch(choice){
case 'A':
case 'a':
printf("Conversion: Decimal to binary and octal.\n");
printf("Enter number:\n");
scanf("%ld", &n);
printf("%ld is ", n);
for (c =28; c >= 0; c--){
k = n >> c;
if (k & 1)
printf("1");
else
printf("0");
}
printf(" in Binary Form. \n");
printf("%ld is ", n);
while (n != 0)
{
o=o+(n%8)*place;
n=n/8;
place=place*10;
}
printf("%ld in Octal Form.\n\n", o);
break;
case 'b':
case 'B':
printf("Conversion: Octal to decimal and binary.\n");
printf("Enter number:\n");
scanf("%ld", &n);
printf("%ld is ", n);
for (c =28; c >= 0; c--)
{
k = n >> c;
if (k & 1)
printf("1");
else
printf("0");
}
printf(" in Binary Form.\n", n, k);
printf("%ld is ", n);
while(n!=0)
{
r=n%10;
dec=dec+r*(pow (8, e));
n=n/10;
e++;
}
printf("%ld in Decimal Form.\n", dec);
default:
printf("Exit.\n\n");
break;
}
}while(choice == 'a'|| choice =='A'|| choice == 'b'|| choice =='B');
return 0;
}

Answer 1

If I run the program with choice 'a' and enter 12, it returns:
12 is 00000000000000000000000001100 in Binary Form.
12 is 14 in Octal Form.
and if I do it again:
12 is 00000000000000000000000001100 in Binary Form.
12 is 1414 in Octal Form.
This is what you should tell us that level of detail as part of the question.
The minimal(ish) fix is to move the variables you initialize into the loop:
int main() {
char choice;
do {
int c, k, r=0, e=0, dec=0, o=0, place=1;
long n;
char new, d;
...
I moved all the declarations even though only the ones that were initialized were required to be moved. This reduces the scope of variables which usually a good practice.
Here are some other suggestions:
Both your switch and the last while loop check for the same thing. If use a if-else if loop instead you can use break to exit the loop. The other option is set a done indicator variable and check that in the loop.
I would also normalize the choice variable, i.e. choice = tolower(choice) so you don't have to check both lower and upper cases.
Consider driving the i/o in the main loop, then call a function that returns data which the main loop then prints out.
Use functions to eliminate duplication (i.e. the binary algorithm should probably be a separate function).
The binary algorithm looks wrong, btw, why does it loop 29 times? You pass it a long which might be 64 bits (at least it is on my system).
You read (signed) long but don't deal with negative values. #WeatherVane.
Value you read, n, doesn't seem to be validated. Should be able to type 'a' for a decimal or octal value? Or 9 for an octal value? Related to that, scanf() can fail so check what it returns.
You say 'd' exits but program logic is anything but 'a' or 'b' (in lower or uppercase) exits.
Formatting matters to people reading your code, so fix the wrong indentation of for (c =28; c >= 0; c--){. I would also suggest you use tab (or 8 spaces). This will encourage you to minimize how many levels you indent your code.