If you're a beginning programmer and want to get more deeply into programming with variables, you've come to the right place. This article, the first of three parts, is excerpted from chapter two of the book Beginning C, written by Ivor Horton (Apress, 2004; ISBN: 1590592530).

First Steps in (C) Programming, introduction - Try It Out: Division and the Modulus Operator (Page 8 of 8 )

Suppose you have a jar of 45 cookies and a group of 7 children. You’ll share out the cookies equally among the children and work out how many each child has. Then you’ll work out how many cookies are left over.

/* Program 2.6 Cookies and kids */ #include <stdio.h> void main() { int cookies = 45; /* Number of cookies in the jar */ int children = 7; /* Number of children */ int cookies_per_child = 0; /* Number of cookies per child */ int cookies_left_over = 0; /* Number of cookies left over */ /* Calculate how many cookies each child gets when they are divided up */ cookies_per_child = cookies/children; /* Number of cookies per child */ printf("You have %d children and %d cookies", children, cookies); printf("\nGive each child %d cookies.", cookies_per_child); /* Calculate how many cookies are left over */ cookies_left_over = cookies%children; printf("\nThere are %d cookies left over.\n", cookies_left_over); }

When you run this program you’ll get this output:

-------------------------------------------- You have 7 children and 45 cookies Give each child 6 cookies. There are 3 cookies left over. --------------------------------------------

HOW IT WORKS

Let’s go through this program step by step. Four integer variables,cookies,children,cookies_per_child, andcookies_left_over, are declared and initialized with the following statements:

int cookies = 45; /* Number of cookies in the jar */ int children = 7; /* Number of children */ int cookies_per_child = 0; /* Number of cookies per child */ int cookies_left_over = 0; /* Number of cookies left over */

The number of cookies is divided by the number of children by using the division operator/to produce the number of cookies given to each child:

cookies_per_child = cookies/children; /* Number of cookies per child */

The next two statements output what is happening, including the value stored incookies_per_child:

printf("You have %d children and %d cookies", children, cookies); printf("\nGive each child %d cookies.", cookies_per_child);

You can see from the output thatcookies_per_childhas the value 6. This is because the division operator always produces an integer result when the operands are integers. The result of dividing 45 by 7 is 6, with a remainder of 3.

You calculate the remainder in the next statement by using the modulus operator:

cookies_left_over = cookies%children;

The expression to the right of the assignment operator calculates the remainder that results when the value ofcookiesis divided by the value ofchildren.

Finally, you output the reminder in the last statement:

printf("\nThere are %d cookies left over.\n", cookies_left_over);

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More on Division with Integers

Let’s look at the result of using the division and modulus operators where one or the other of the operands is negative. With division, if the operands have different signs, the result will be negative. Thus, the expression –45/7 produces the same result as the expression 45/–7, which is –6. If the operands in a division are of the same sign, then the result is positive. Thus, 45/7 produces the same result as –45/–7, which is 6.

With the modulus operator, the sign of the result is always the same as the sign of the left operand. Thus, 45%–7 results in the value 3, whereas –45%7 results in the value –3.

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