Else If In C

Else If In C

The construction
if (expression)
statement
else if (expression)
statement
else if (expression)
statement
else if (expression)
statement
else
statement
occurs so often that it is worth a brief separate discussion. This sequence of if statements is the most
general way of writing a multi-way decision. The expressions are evaluated in order; if an expression is
true, the statement associated with it is executed, and this terminates the whole chain. As always, the
code for each statement is either a single statement, or a group of them in braces.
The last else part handles the ``none of the above'' or default case where none of the other conditions is

satisfied. Sometimes there is no explicit action for the default; in that case the trailing
else
statement
can be omitted, or it may be used for error checking to catch an ``impossible'' condition.
To illustrate a three-way decision, here is a binary search function that decides if a particular value x
occurs in the sorted array v. The elements of v must be in increasing order. The function returns the
position (a number between 0 and n-1) if x occurs in v, and -1 if not.
Binary search first compares the input value x to the middle element of the array v. If x is less than the
middle value, searching focuses on the lower half of the table, otherwise on the upper half. In either case,
the next step is to compare x to the middle element of the selected half. This process of dividing the

range in two continues until the value is found or the range is empty.

/* binsearch: find x in v[0] <= v[1] <= ... <= v[n-1] */

int binsearch(int x, int v[], int n)

{

int low, high, mid;

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 /* found match */

return mid;

}

return -1; /* no match */

}

The fundamental decision is whether x is less than, greater than, or equal to the middle element v[mid]
at each step; this is a natural for else-if.