Why does my program not add numbers until -1 is given?

Question

The following code should prompt the user for prices and add that to a total. If the user inputs -1 the adding loop must terminate and the program should print a total and exit. But for some reason this is not happening.

#include <stdio.h>
int main()
{
  int price;
  int sum;
  int exit;

  do
  {
    printf(" Enter a price(-1 to exit)");
    scanf("%d", & price);
    sum = sum + price++;

    printf("the sum of prices is % d ", sum);
  }
  while (exit != -1);

  return 0;
}

Q: Why does my program not add numbers until -1 is given?

The best thing to do is see one of the teacher's assistants, and go through this code line by line. — user3386109, Nov 12 '19 at 22:16
Why even have a variable "exit"? After reading price, if it is -1, break from the loop. — FredK, Nov 12 '19 at 22:55
Consider using the more common `while` loop. `while(scanf("%d", &price) == 1 && price >= 0) { sum += price; }` — Weather Vane, Nov 12 '19 at 22:58
What is your question? Stating requirements and showing code which does not match them is not a question. Did you debug? Did you rubber duck it? What problem do you see? What got you stuck? — Yunnosch, Nov 12 '19 at 22:58

score 1 · Answer 1 · answered Nov 12 '19 at 23:12

You aren't assigning exit to anything. If you want the user to enter the string -1, the check if price is -1 and break from the loop. If you meant for the user to enter a character with a value of -1, then use fgetc(stdin), and check if the character is -1.

Also, to calculate the sum correctly, you shouldn't be incrementing price with sum = sum + price++;. If this was meant to circumvent the situation where price is -1 and you don't want to subtract from the sum, you should check if exit is -1 inside the loop, and use the break keyword.

It isn't the largest issue, but you should be formatting your code according to conventions (e.g. indenting properly, address-of-operator next to the identifier, etc).

score 1 · Accepted Answer · answered Nov 13 '19 at 04:58

1

You should use if-else statement to resolve it. Like shown below:

while(price != -1)
{
    printf(" \nEnter a price(-1 to exit)");
    scanf("%d", &price);
    if (price == -1)
    {
      break;
    }
    else{
        sum = sum + price;
        printf(" \ntotal sum till now is %d", sum);
    }
}

answered Nov 13 '19 at 04:58

Himanshu Singh

2,117
1
5
15

You should use ```while(1)``` or ```for(;;)``` if you break out of the loop internally. – reeeee Nov 20 '19 at 23:42

score 0 · Answer 3 · answered Nov 13 '19 at 00:07

Hello man look now in what is the problem u named a int exit right ? But you only make exit only int varible and the memory is unfiltered so the computer get a memory from something else and its not a -1 you need to put the %d price in the wile

int price;
do
{
 block_of_command
}
While(price!=-1);

Or

int exit;
int price
do
{
scanf("%d",&price);
exit=price;
}
while(exit!=-1);

sweet · Answer 4 · 2019-11-13T00:23:56.223

0

i updated the code but i dont know how to add all the user inputted prices before exiting. here is my code.

#include<stdio.h>
int main()
{
int price;
int sum = 0;

while(price != -1)
{
    printf(" Enter a price(-1 to exit)");
    scanf("%d", & price);


    if (price == -1)
    {
      sum = sum + price;
      printf(" adds is %d", sum);
      break;
    }

   }



  return 0; 
  }

edited Nov 13 '19 at 00:23

answered Nov 13 '19 at 00:17

sweet

11
3

Use if-else to differentiate the two cases. 1) to add user input 2) to break loop and exit. Just for reference I have added coffee snippet in answer below. – Himanshu Singh Nov 13 '19 at 05:05

Why does my program not add numbers until -1 is given?

4 Answers4