nullIntroduction to Computer
(C Programming)Introduction to Computer
(C Programming)Software College , Northeastern University
2010,9
Chapter3 Operators and Expressions 3.1 introduction 3.1 introduction C operators can be classified into a number of categories. They include:
Arithmetic operators.
Relational operators.
Logical operators.
Assignment operators.
Increment and decrement operators.
Conditional operators.
Bitwise operators.
Special operators.3.2 Arithmetic operators 3.2 Arithmetic operators Operator Meaning
＋ Addition or unary plus
－ Subtraction or unary minus
＊ Multiplication
／ Division
％ Modulo division Examples:
a-b, a+b, a*b, a/b, a%bExample 3.1Example 3.1The Program shows the use of integer arithmetic to convert a given number of days into months and days.main()
{
int months, days;
printf(“Enter days\n”);
scanf(“%d”, &days);
months = days/30;
days = days % 30;
printf(“Months=%d days=%d”, months, days);
}
Output
Enter days
265
Months=8 Days=25
Enter days
364
Months=12 Days=4
Enter days
45
Months=1 Days=153.3 Relational Operators3.3 Relational OperatorsC supports six relational operators in all:
Operators Meaning
< is less than
<= is less than or equal to
> is greater than
>= is greater than or equal to
== is equal to
!= is not equal toExample
4.5<=10 4.5<-10 -35>=0
10<7+5 a+b==c+d ?Relational Operator ComplementsRelational Operator Complements Among the six relational operators, each one is a complement of another operator.
> is complement of <=
< is complement of >=
== is complement of !=
We can simplify an expression involving the not and the less than operators using the complements as shown below:
Actual one Simplified one
!(x=y
!(x>y) x<=y
!(x!=y) x==y
!(x<=y) x>y
!(x>=y) xb && x==10
Truth TableTruth Table Op_1 Op_2 Value of the Expression
op_1&&op_2 op_1||op_2
Non_zero Non_zero 1 1
Non_zero 0 0 1
0 Non_zero 0 1
0 0 0 0Examples:
1. if (age > 55 && salary < 1000)
2. if (number < 0 || number > 1000) 3.5 Assignment Operators3.5 Assignment OperatorsC has a set of ‘shorthand’ operators of the form:
v op =exp;
where v is a variable,
exp is an expression
op is a C binary arithmetic operator
op= is known as the shorthand assignment operator
v op =exp; is equivalent to v =v op (exp);Examples:
x+=y+1; is equivalent to x=x+(y+1);
x+=3; is equivalent to x=x+3;Shorthand Assignment OperatorsShorthand Assignment Operators Statement with simple Statement with
assignment operator shorthand operator
a = a + 1 a += 1
a = a – 1 a -= 1
a = a * (n+1) a *= n+1
a = a / (n+1) a /= n+1
a = a % b a %= bThe use of shorthand assignment operators has three advantages:The use of shorthand assignment operators has three advantages:What appears on the left-hand side need not be repeated and therefore it becomes easier to write.
The statement is more concise and easier to read
The statement is more efficientExample:
value = value+ delta;
With the help of the += operator, this can be written as follows: value += delta;Example 3.2Example 3.2The Program prints a sequence of squares of numbers. Note the use of the shorthand operator *=.#define N 100
#define A 2
main()
{
int a;
a = A;
while(a b) ? a : b;
if (a > b) x = a; else x = b;3.8 Bitwise Operator3.8 Bitwise OperatorC has a distinction of supporting special operators known as bitwise operators for manipulation of data at bit level. These operators are used for testing the bits, or shifting them right or left. Bitwise operators may not applied to float or double. Operator Meaning
& bitwise AND
| bitwise OR
^ bitwise exclusive OR
<< shift left
>> shift right3.9 Special Operators3.9 Special OperatorsPointer Operators:
& and *
Member Selection Operators:
. and ->nullThe Comma Operator:
can be used to link the related expression together. A comma-linked list of expressions are evaluated left to right and the value of right-most expression is the value of the combined expression.
Example: value = (x = 10, y = 5, x + y);
value = 15;
Some applications of comma operator are:
In for loops: for ( n = 1, m = 10; n <= m; n++, m++ )
In while loops: while( c = getchar( ), c != ‘\n’ )
Exchanging values: t = x, x = y, y = t;
nullThe sizeof Operator:
is a compile time operator and, when used with an operand, it returns the number of bytes the operand occupies. The operand may be a variable, a constant or a data type qualifier.
Example:
m = sizeof (sum);
n = sizeof (long int);
k = sizeof(235L);Note: The sizeof operator is normally used to determine the lengths of arrays and structures when their sizes are not known to the programmer. It is also used to allocate memory space dynamically to variables during of a program
Example 3.3Example 3.3The program employs different kinds of operators. The results of their evaluation are also shown for comparison.main()
{
int a, b, c, d;
a = 15;
b = 10;
c = ++a – b;
printf(“a=%d b=%d c=%d\n”,a,b,c);
d = b++ +a;
printf(“a=%d b=%d d=%d\n”,a,b,d);
printf(“a/b = %d\n”, a/b);
printf(“a%%b = %d\n”, a%b);
printf(“a*=b = %d\n”, a*=b);
printf(“%d\n”, (c>d)?1:0);
printf(“%d\n”, (c
main ( )
{
int a,b,k;
k=(a=2,b=5,a>b?a++:b++,a+b);
printf("k = %d\n", k);
}k = 8运行结果：课堂练习课堂练习给出下面程序的输出结果：[短路现象]#include
main ( )
{
int a=1,b=2,c=3,d=4,m=1,n=1;
(m=a>b)&&(n=c>d);
printf("m = %d\n", m);
printf("n = %d\n", n);
}m = 0
n = 1运行结果：
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