Chapter 7
Simple Data
Types and
Function Calls
Yuksel / Demirer
Representation and Conversion of
Numeric Types
• Simple data type is the data type used to store a
single value.
– e.g., int, double, and char.
• Operations involving integer are faster than
those involving double.
• Operations with integer are always precise,
whereas loss of accuracy may occur when
dealing with double.
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7-2
Internal Formats of Type int and
Type double
• Integers are represented by standard binary
numbers.
– e.g., 7 = 01101.
• Doubles are represented by two sections:
mantissa and exponent.
– real number = mantissa * 2exponent
– 4.0 = 0010 * 20001 = 2 * 21
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Integer Types in C
Type
Range
short
-32767 .. 32767
unsigned short
0 .. 65535
int
-32767 .. 32767
unsgined
0 .. 65535
long
-2147483647 .. 2147483647
unsgined long
0 .. 4294967295
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7-4
Floating-Point Types in C
Type
Range
float
10-37 .. 1038
double
10-307 .. 10308
long double
10-4931 .. 104932
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7-5
An Example to Print Ranges for
Positive Numeric Data
You can determine the maximal or minimal int and
double values of your C environment by the following
program.
%e is the format in
scientific notation
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7-6
Numerical Inaccuracies
• The representation error (or round-off
error) is an error due to coding a real
number by a finite number of digits.
– e.g., the fraction of 1/3 is 0.3333…
– It is impossible to code the precise value of
1/3.
• The representation error depends on the
number of digits used in the mantissa.
– The more bits, the smaller the error.
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7-7
An Example of the Representation
Error
• for (trial = 0.0;
trial != 10.0;
trial = trial + 0.1) {
…
}
• The result of adding 0.1 for one hundred times is
not exactly 10.0.
– The above loop may fail to terminate on some
computers.
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7-8
Other Problems When Manipulating
Numbers
• Cancellation error is an error resulting from
applying an operation to a large number and a
small number, and the effect of the smaller
number is lost.
– e.g., 1000.0 + 0.0000001234 is equal to 1000.0.
• Arithmetic underflow is an error in which a
very small computational result is represented as
zero.
– e.g., 0.00000001 * 10-1000000 is equal to 0.
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7-9
Other Problems When Manipulating
Numbers
• Arithmetic overflow is an error in which the
result is too large to be represented.
– The error may be detected in compiling time or run
time.
– Some machine may let the arithmetic overflow occur
and the computational result is unexpected.
– e.g., 999999999 * 109999999 may become a negative
value in some machine.
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7-10
Automatic Conversion of Data Types
(1/2)
• The data of one numeric type may be automatically
converted to another numeric type.
e.g.,
int k = 5, m = 4, n;
double x = 1.5, y = 2.1, z;
Context
Expression with
binary operator
and operands of
different types
Example
k + x
value is 6.5.
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Explanation
Value of k is
converted to
double before
the operation.
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Automatic Conversion of Data Types
(2/2)
Context
Example
Explanation
z = k / m;
Assignment with
type double target expression value
is 1.25; z is 1.0.
variable and type
int expression
Expression is
evaluated first.
Then the result is
converted to
double.
n = x * y;
Assignment with
type int target
expression value
is 3.15; n is 3.
variable and type
double expression
Expression is
evaluated first.
Then the result is
converted to int.
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7-12
Explicit Conversion of Data Types
• C also provides an explicit type conversion
operation called cast.
• For example, frac = n1 / d1;
if n1 = 2 and d1 = 4, frac would be 0.
• Cast: place the name of the desired type in
parentheses immediately before the value to be
converted.
– e.g., frac = (double)n1 / (double)d1;
– frac is evaluated to 0.5.
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7-13
Representation and Conversion of
Type char (1/2)
• Character values can be compared by the
equality operators == and !=, or by the
relational operators <, <=, >, and >=.
e.g., letter = ‘A’;
if (letter < ‘Z’) …
• Character values may also be compared,
scanned, printed, and converted to type int.
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7-14
Representation and Conversion of
Type char (2/2)
• Each character has its own unique numeric code.
• A widely used standard is called American
Standard Code for Information Interchange
(ASCII). (See Appendix A in the textbook)
– The printable characters have codes from 32 to
126, and others are the control characters.
– For example, the digit characters from ‘0’ to ‘9’ have
code values from 48 to 57 in ASCII.
• The comparison of characters (e.g., ‘a’<‘c’)
depends on the the corresponding code values in
ASCII.
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7-15
An Example of the Conversion
between char and int
C permits conversion of type char to type int
and vice versa.
Convert char to int
Convert int to char
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7-16
Enumerated Types (1/2)
• Enumerated type is a data type whose list of
values is specified by the programmer.
• Syntax: typedef enum
{identifier_list}
enum_type;
• e.g.,
typedef enum
{entertainment, rent, food,
clothing}
expense_t;
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7-17
Enumerated Types (2/2)
• In the above example, a new data type expense_t is
created, and we can declare a variable with this type:
e.g., expense_t expense_kind;
• The variable expense_kind can be manipulated as
any other integer.
e.g., switch(expense_kind){
case entertainment:
printf(“entertainment”);
break;
case rent:
case food:
…
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7-18
Functions: Arguments are passed by
values
• Argument lists are used to communicate information from the
main function to its function subprograms.
– Arguments make functions more versatile because they allow us
to execute the same function with different sets of data.
• Return values are used to communicate information from the
function subprogram back to the main program.
• We can use output parameters to return multiple results from
a function.
• When a function is called, it is given a copy of the values that
are passed in as arguments.
– If you manipulate the value of an argument, it has no impact on
its value in the main function
– Therefore, these are called input parameters, because they can
only bring information into the function, and not back out.
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7-19
Function Parameters (1/2)
• When invoking a function call, we can include
function parameters in the parameter list.
• Declaring a function parameter is
accomplished by simply including the prototype
of the function in the parameter list.
A function parameter
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7-20
Function Parameters (2/2)
• Suppose there are two existed functions:
double sqrt(double) , and
double sin(double).
• evaluate is a function that includes a function
parameter as shown in the previous slide.
• We can invoke evaluate as follows.
evaluate(sqrt, 0.25, 25.0,
100.0);
evaluate(sin, 0.0, 3.14159,
0.5*3.14159);
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7-21
Example with pass by value
void myFunc(int arg);
int main(void)
{
int x = 5;
myFunc(x);
printf(“%d\n”, x);
}
void myFunc(int arg)
{
arg = 4;
}
/* Output */
5
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7-22
In main: int x = 5;
In main, x is assigned the value 5.
This places the value 5 in the memory cell reserved for x
In this case, it is at address 0x234
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7-23
In main: myFunc(x);
We call the function myFunc and pass it the value of x
myFunc allocates a new memory cell for its formal parameter arg
The value 5 (a copy of the value in x) is placed in arg
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7-24
In myFunc: arg = 4;
In myFunc, arg is assigned the value of 4
This places the value 4 in the memory cell for arg
This is not the same cell as x
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7-25
In main: printf(“%d\n”, x);
Back in main, when we print out x, the value it points to
is still 5.
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7-26
Functions: Arguments are passed by Reference
• What if we want our changes to the value in the function to
affect the value in the main function?
• We can accomplish that by passing the address of a variable as
argument to a function and manipulate that variable inside the
function.
• In the formal parameter list, we put a * in front of the parameter
name.
– This defines a pointer, which means that we will be passing the address
of the value, rather than the value itself.
• In the function call, we put an & in front of the argument name.
– The & tells the compiler to pass the address of the variable, not its
value.
• When we need to access the value of the argument in the
function, we put a * in front of the variable name
– This * tells the compiler to access the value pointed to by the address in
the variable.
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7-27
Example with pass by reference
void myFunc(int* arg);
int main(void)
{
int x = 5;
myFunc(&x);
printf(“%d\n”, x);
}
void myFunc(int* arg)
{
*arg = 4;
}
/* Output */
4
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7-28
In main: int x = 5;
In main, x is assigned the value 5, just like before.
The address of the memory cell for x is 0x234
The value of &x is 0x234
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7-29
In main: myFunc(&x);
When we call myFunc, we pass it &x, the address of x
This value is stored in the memory cell for arg.
arg == 0x234, *arg == 5
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7-30
In myFunc: *arg = 4;
When we set the value of *arg, we are setting the value
pointed to by arg – the value at 0x234
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7-31
In main: printf(“%d\n”, x);
Back in main, the value of x is now 4
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7-32
#include <stdio.h>
#include <math.h>
void separate(double num, char *signp, int *wholep,
double *fracp);
int main(void)
{
double value, fr;
char sn;
int whl;
printf("Enter a value to analyze> ");
scanf("%lf", &value);
separate(value, &sn, &whl, &fr);
printf("Parts of %.4f\n sign: %c\n", value, sn);
printf(" whole number magnitude: %d\n", whl);
printf(" fractional part: %.4f\n", fr);
return 0;
}
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7-33
void separate(double num, char *signp, int *wholep,
double *fracp)
{
double magnitude;
if (num < 0)
*signp = ’-’;
else
if (num == 0)
*signp = ’ ’;
else
*signp = ’+’;
magnitude = fabs(num);
*wholep = floor(magnitude);
*fracp = magnitude - *wholep;
}
Parts of 35.8170
sign: +
whole number magnitude: 35
fractional part: 0.8170
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7-34
Figure 6.4 Parameter Correspondence for
separate(value, &sn, &whl, &fr);
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Common Errors with Pointers
• Note that this is a run-time error. It will not cause a
compiler error.
• Therefore, make sure you set a pointer equal to the
address of some variable (of the correct type!) before
you attempt to use it.
ERROR!
• For example:
double x = 10.0, y = 20.0,
p_x = &x;
This will cause the program
to crash as p_y has not
been initialized.
*p_x, *p_y;
printf(“x = %f and y = %f\n”, *p_x, *p_y);
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7-36
The Conditional Expression Operator
• Condition ? expression 1: expression 2
• Max_value = (a>b) ? a : b;
• S = (x <0) ? -1 : x*x
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7-37
Scope of Names
• The scope of a name refers to the region of a program where a
particular meaning of a name is visible or can be referenced.
• #define variables scope begins at their definition and ends at the
end of the source file. All functions can “see” these variables.
• The scope of the name of a function begins with the function
prototype and ends with the end of the source file.
• All formal parameter names and local variables are visible only
from their declarations to the closing brace of the function in
which they are declared.
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7-38