My binary search program compiles, but something is wrong with my algorithm. For example, if I try to find 9 in the list 2 5 7 8 9 10, my program says that there is no 9 in the list. Where have I gone wrong?
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
int valuetofind, n, list [100];
bool found, notinthelist;
int binary_search () {
int middle, p = 0, q = n-1;
middle = (p + q) / 2;
while ( (found == false) && (notinthelist == false) ) {
if (list[middle] == valuetofind) {
found = true;
printf("%d is the %d element\n", valuetofind, middle+1);
}
else {
if (n < list[middle] ) q = middle - 1;
else p = middle + 1;
if (p > q) {
notinthelist = true;
printf("%d is not in this list\n", valuetofind);
}
}
middle = (p + q) / 2;
}
}
int main () {
found = false;
notinthelist = false;
printf("How many elements are there in your list?\n");
scanf("%d", &n);
for (int i = 0; i<n; i++){
scanf("%d", &list[i]);
}
printf("What value do you want to find?\n");
scanf("%d", &valuetofind);
binary_search();
}
Change
if (n < list[middle] ) q = middle - 1;
to
if (valuetofind < list[middle] ) q = middle - 1;
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