Loop repeating scanf and printf - c

Question

I've written a program that will scanf twice before printf and will output two of what should be a single printf. The issue seems to begin occurring from the point that asks the user to input a number between 1 to 4 to see the average temperature for the entered number of days.
I'm not sure what's causing this double inputs and outputs and the occasional delays. Here's my code:
#include <stdio.h>
#include <stdlib.h>
int main (void) {
int i;
int limit;
int day[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int high[10], low[10];
printf("---===IPC Temperature Analyzer V2.0===---\n");
printf("Please enter the number of days between 3 and 10, inclusive: ");
scanf("%d", &limit);
while (limit <= 2 || limit >= 11) {
printf("Invalid entry, please enter a number between 3 and 10, inclusive: ");
scanf("%d", &limit);
}
for (i = 0; i < limit; i++) {
printf("Day %d - High: ", day[i]);
scanf("%d", &high[i]);
printf("Day %d - Low: ", day[i]);
scanf("%d", &low[i]);
}
printf("\nDay Hi Low\n");
for (i = 0; i < limit; i++) {
printf("%d %d %d\n", day[i], high[i], low[i]);
}
int max = 0;
int min = 0;
for (i = 0; i < limit; i++) {
if (high[max] < high[i])
max = i;
if (low[min] > low[i])
min = i;
}
printf("\nHighest temperature was: %d on day %d\n", high[max], day[max]);
printf("Lowest temperature was: %d on day %d\n", low[min], day[min]);
int n;
do {
printf("\nEnter a number between 1 and 4 to see the average temperature "
"for the entered number of days, enter a negative number to exit:");
scanf("%d\n", &n);
while (n > 4) {
printf("Invalid entry, please enter a number between 1 and 4, inclusive: ");
scanf("%d", &n);
}
while (n < 0) {
printf("Goodbye!\n");
exit(0);
}
float avgSum = 0.0;
for (i = 0; i < n; i++) {
float avgOfDay = (high[i] + low[i]) / 2.0;
avgSum += avgOfDay;
}
float overallAvg = avgSum / n;
printf("The average temperature up to day %d is: %.2f\n", day[n - 1], overallAvg);
} while (n > 0 || n < 4);
return 0;
}
Example output:
Enter a number between 1 and 4 to see the average temperature for the entered number of days, enter a negative number to exit:5
5
Invalid entry, please enter a number between 1 and 4, inclusive: Invalid entry, please enter a number between 1 and 4, inclusive: 3
The average temperature up to day 3 is: 2.50
Enter a number between 1 and 4 to see the average temperature for the entered number of days, enter a negative number to exit: 2
2
The average temperature up to day 2 is: 2.75
Enter a number between 1 and 4 to see the average temperature for the entered number of days, enter a negative number to exit: -1
The average temperature up to day 2 is: 2.75
Enter a number between 1 and 4 to see the average temperature for the entered number of days, enter a negative number to exit: -1
Goodbye!

Answer 1

The problem you are describing can be traced to the scanf() statement at the beginning of the do loop:
scanf("%d\n", &n);
The newline at the end of the format string is the trouble. When scanf() encounters a white-space character in the format string, it matches white-space characters in the input stream until a non-white-space character is encountered. The problem is that when you press the enter key to input your number, this is just another white-space character, so scanf() greedily continues waiting for more input, until either a non-white-space character, or EOF is encountered. When the user enters a non-white-space character at this point, the scanf() white-space match fails, the entered character remains in the input stream, scanf() finally returns to the calling function, and at last, the next scanf() picks up the character that was just rejected. This is the cause of the sporadic response that you observed.
The fix for this is simple. Just remove the \n from the end of the format string. It is usually the case that a white-space character at the end of a format string is the wrong thing to do.
There are other issues in the code. The test at the end of the do loop should be:
while (n > 0 && n < 4);
The test for an exit value would be better as an if statement instead of a while loop, and the test should be for n < 1 instead of n < 0 to avoid a division by zero error:
if (n < 1) {
printf("Goodbye!\n");
exit(0);
}
It seems that you should change the input prompt to:
printf("\nEnter a number between 1 and 3 to see the average temperature for the entered number of days, enter a negative number to exit:");
If the user chooses 4 here, but only entered data for 3 days, the calculation will access uninitialized values in the high[] and low[] arrays. You will also need to change this input loop to:
while (n > 3) {
printf("Invalid entry, please enter a number between 1 and 3, inclusive: ");
scanf("%d", &n);
}
There may be other issues, but this should get things running.

Answer 2

while (n > 0 || n < 4); => while (n > 0 && n < 4);

Answer 3

I was able to determine the solution to my problem. The new line function next to the scanf and printf of some parts of my code were causing the program to reiterate certain scanf and printf functions.
scanf("%d\n", &n) =>
printf("%d", &n)
printf ("The average temeprature up to day %d is: %.2f\n", day[n-1], overallAvg); =>
printf ("The average temeprature up to day %d is: %.2f", day[n-1], overallAvg);