Other than in a for statement, when is the comma operator used? Ans. The comma operator is commonly used to separate variable declarations, function arguments, and expressions, as well as the elements of a for statement. Look closely at the following program, which shows some of the many ways a comma can be used: #include #include void main(void); void main() { /* Here, the comma operator is used to separate three variable declarations. */ int i, j, k; /* Notice how you can use the comma operator to perform multiple initializations on the same line. */ i = 0, j = 1, k = 2; printf('i = %d, j = %d, k = %d\n', i, j, k); /* Here, the comma operator is used to execute three expressions in one line: assign k to i, increment j, and increment k. The value that i receives is always the rightmost expression. */ i = (j , k ); printf('i = %d, j = %d, k = %d\n', i, j, k); /* Here, the while statement uses the comma operator to assign the value of i as well as test it. */ while (i = (rand() % 100), i != 50) printf('i is %d, trying again...\n', i); printf('\nGuess what? i is 50!\n'); } Notice the line that reads i = (j , k ); This line actually performs three actions at once. These are the three actions, in order: 1. Assigns the value of k to i. This happens because the left value (lvalue) always evaluates to the rightmost argument. In this case, it evaluates to k. Notice that it does not evaluate to k , because k is a postfix incremental expression, and k is not incremented until the assignment of k to i is made. If the expression had read k, the value of k would be assigned to i because it is a prefix incremental expression, and it is incremented before the assignment is made. 2. Increments j. 3. Increments k. Also, notice the strange-looking while statement: while (i = (rand() % 100), i != 50) printf('i is %d, trying again...\n'); Here, the comma operator separates two expressions, each of which is evaluated for each iteration of the while statement. The first expression, to the left of the comma, assigns i to a random number from 0 to 99. The second expression, which is more commonly found in a while statement, is a conditional expression that tests to see whether i is not equal to 50. For each iteration of the while statement, i is assigned a new random number, and the value of i is checked to see that it is not 50. Eventually, i is randomly assigned the value 50, and the while statement terminates.

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