C程序设计语言（第二版） 3-1

3-1 折半查找，2个版本

int binsearch(int x, int v[], int n) { 
    int low, mid, high; 
     
    low = 0; 
    high = n - 1; 
    while ( low <= high ) { 
        mid = (low+high) / 2; 
        if ( x < v[mid] ) 
            high = mid - 1; 
        else if ( x > v[mid] ) 
            low = mid + 1; 
        else 
            return mid; 
    } 
    return -1; 
} 

 
int binsearch2(int x, int v[], int n) { 
    int low, high, mid; 
     
    low = 0; 
    high = n - 1; 
    mid = (low+high) / 2; 
    while ( low <= high && x != v[mid] ) { 
        if ( x < v[mid] ) 
            high = mid - 1; 
        else 
            low = mid + 1; 
        mid = (low+high) / 2; 
    } 
    if ( x == v[mid] ) 
        return mid; 
    else 
        return -1; 
}