4. EXPRESSIONS

Display the value of pi, 3.14159265 to 5 decimal places, right justified, in 9 columns

Read in someone’s height in feet and inches using a single quotation mark for feet and double quotation mark for inches and prints the person’s height in centimeters to two decimal places

/* Computes a Universal Product Code check digit */ #include <stdio.h>

int main(void)

{

int d, i1, i2, i3, i4, i5, j1, j2, j3, j4, j5, first_sum, second_sum, total;

printf("Enter the first (single) digit: ");

scanf("%1d", &d);

printf("Enter first group of five digits: "); scanf("%1d%1d%1d%1d%1d", &i1, &i2, &i3, &i4, &i5);

printf("Enter second group of five digits: "); scanf("%1d%1d%1d%1d%1d", &j1, &j2, &j3, &j4, &j5);

first_sum = d + i2 + i4 + j1 + j3 + j5;

second_sum = i1 + i3 + i5 + j2 + j4;

total = 3 * first_sum + second_sum;

printf("Check digit: %d\n", 9 - ((total - 1) % 10));

return 0;

}

Arithmetic Operators• The arithmetic operators are:

+ unary plus

- unary minus

+ addition

- subtraction

* multiplication

/ division

% remainder (modulus)

Arithmetic Operators• The value of i % j is the remainder when i is divided

by j. For example, the value of 10 % 3 is 1; the value of 12 % 4 is 0. The % operator requires integer operands; all other operators allow either integer or floating-point operands.

• If both operands are integers, / truncates the result toward 0.

• There is no exponentiation operator.•Must use “pow” function defined in <math.h>

Operator Precedence• When an expression contains more than one operator,

the meaning of the expression may not be immediately clear:

Does i + j * k mean (i + j) * k or i + (j * k) ?

• In C, this potential ambiguity is resolved by operator precedence.

• Precedence of the arithmetic operators:

Highest: + - (unary)

* / %

Lowest: + - (binary)

Operator Precedence• Examples:

i + j * k means i + (j * k)

-i * -j means (-i) * (-j)

+i + j / k means (+i) + (j / k)

Associativity• Operator precedence rules alone aren’t enough when an

expression contains two or more operators at the same level of precedence. The associativity of the operators now comes into play.

• The binary arithmetic operators are all left associative (they group from left to right); the unary operators are right associative.

• Examples of associativity:

i - j - k means (i - j) - ki * j / k means (i * j) / ki - j * i + k means (i - (j * i)) + k- - i means -(-i)

Simple Assignment• One way to change the value of a variable is by assignment.

• Simple assignment has the form v = e, where v is an lvalue and e is an expression. Examples:

i = 5; /* i is now 5 */j = i; /* j is now 5 */k = 10 * i + j; /* k is now 55 */

• If v and e don’t have the same type, then the value of e is converted to the type of v before assignment:

int i;float f;i = 72.99; /* i is now 72 */f = 136; /* f is now 136.0 */

Simple Assignment (Continued)• Assignment is a true operator, just like + and *. The value of v = e is the value of v after the assignment.

• Assignments can be chained together: i = j = k = 0;

• Since the = operator is right associative, this statement is equivalent to i = (j = (k = 0));

• The assignment operator may appear in any expression:

i = 1;k = 1 + (j = i);printf("%d %d %d\n", i, j, k); /* prints "1 1 2" */

•Hiding an assignment inside a larger expression usually isn’t a good idea.

Lvalues• The increment and decrement operators require an lvalue (pronounced “Lvalue”) as their operand.

• An expression has an lvalue if it represents a storage location in computer memory.

• Variables are lvalues, since a variable is just a name for a storage location.

• Constants and most expressions containing operators are not lvalues, including the following:

12i + j-i

Compound Assignment

• In addition to the simple assignment operator =, C provides ten compound assignment operators, including these five:

+= -= *= /= %=

• The expression v += e is equivalent to v = v + e,

except that v is evaluated only once in the former expression. The other operators have similar meanings.

Increment and Decrement Operators

• The ++ and -- operators increment and decrement variables.

• Both operators have the same precedence as negation.

• Either operator can be prefix or postfix: ++i

i++

--i

i--

• When used as a prefix operator, ++ increments the variable before its value is fetched:

i = 1;

printf("i is %d\n", ++i); /* prints "i is 2" */

Increment and Decrement Operators

• When used as a postfix operator, ++ increments the variable after its value is fetched:

i = 1;

printf("i is %d\n", i++); /* prints "i is 1" */

printf("i is %d\n", i); /* prints "i is 2" */

• The -- operator has similar properties: i = 1;

printf("i is %d\n", --i); /* prints "i is 0" */

i = 1; printf("i is %d\n", i--); /* prints "i is 1" */

printf("i is %d\n", i); /* prints "i is 0" */

Compound AssignmentExamples:i = 5;j = 2;i += j; /* i is now 7 */

i = 5;j = 2;i -= j; /* i is now 3 */

i = 5;j = 2;i *= j; /* i is now 10 */

i = 5;j = 2;i /= j; /* i is now 2 */

i = 5;j = 2;i %= j; /* i is now 1 */

Compound Assignment

• The compound assignment operators have the same properties as the = operator; in particular, they’re right associative and can be used in arbitrary expressions.

Expression Statements

• Any expression can be used as a statement: ++i;

• The value of the expression is discarded; the statement has no effect unless the expression modifies one of its operands:

i = 1; /* stores 1 into i, then evaluates i and discard the result */

i--; /* fetches i, discards the result, then decrements i */

i + j; /* adds i and j, then discards the result */

Expression Statements

• Expression statements are typically used to perform assignments or to increment or decrement variables.

• Warning: A minor typing mistake can turn a meaningful statement into a meaningless expression statement. For example, the statement

i = j;

could easily become

i + j;

Partial List of C OPerators

Precedence Operator Associativity

1 ++ (postfix)-- (postfix)

Left

2 ++ (prefix)-- (prefix)+-

Right

3 */%

Left

4 +-

Left

5 = *= /= %= += -+ right

Expression Evaluation

a = b += c++ - d + --e / -f

Order of subexpression evaluation

a = 5;

c = (b = a + 2) - (a = 1);

#include <stdio.h>

int main()

{

printf("01(a). %d\n", 3 -2 / 4);

printf("01(b). %f\n", 3 -2.0 / 4);

printf("\n02. %d\n", -27 / -5 + 4 / 3);

printf("\n03. %d\n", 16 % -5 + 7 * 6);

printf("\n04(a). %d\n", -12 * 3 % 2 * -23 / +6 - 5 * 2);

float x = 3;

printf("\n05(a). %f\n", x-- * 2 + 5);

printf("05(b). %f\n", x);

printf("05(c). %f\n", --x * 2 + 5);

printf("05(d). %d\n", 3 % 5 / (5 % 3));

return 0;

}