## 数据结构二分搜索程序

```#include <stdio.h>

#define MAX 20

// array of items on which linear search will be conducted.
int intArray[MAX] = {1,2,3,4,6,7,9,11,12,14,15,16,17,19,33,34,43,45,55,66};

void printline(int count) {
int i;

for(i = 0;i < count-1;i++) {
printf("=");
}

printf("=\n");
}

int find(int data) {
int lowerBound = 0;
int upperBound = MAX -1;
int midPoint = -1;
int comparisons = 0;
int index = -1;

while(lowerBound <= upperBound) {
printf("Comparison %d\n" , (comparisons +1) );
printf("lowerBound : %d, intArray[%d] = %d\n",lowerBound,lowerBound,
intArray[lowerBound]);
printf("upperBound : %d, intArray[%d] = %d\n",upperBound,upperBound,
intArray[upperBound]);
comparisons++;

// compute the mid point
// midPoint = (lowerBound + upperBound) / 2;
midPoint = lowerBound + (upperBound - lowerBound) / 2;

// data found
if(intArray[midPoint] == data) {
index = midPoint;
break;
} else {
// if data is larger
if(intArray[midPoint] < data) {
// data is in upper half
lowerBound = midPoint + 1;
}
// data is smaller
else {
// data is in lower half
upperBound = midPoint -1;
}
}
}
printf("Total comparisons made: %d" , comparisons);
return index;
}

void display() {
int i;
printf("[");

// navigate through all items
for(i = 0;i<MAX;i++) {
printf("%d ",intArray[i]);
}

printf("]\n");
}

void main() {
printf("Input Array: ");
display();
printline(50);

//find location of 1
int location = find(55);

// if element was found
if(location != -1)
printf("\nElement found at location: %d" ,(location+1));
else