CHAPTER 3
Overview of C Program
Has five sections as its program structure, namely: the introductorycomments, header files, constant definitions, function definition, andthe main program but In this chapter, only the introductorycomments, header files, constant definitions, and the main programwill be covered.
Arrangement of the parts of a C program:
<Introductory Comments>
<Header Files>
<Constant Definitions>
<Function Definition>
<Main Program>
<Variable Declaration>
<Statements>
|
Introductory comments:
Contain the name of the author, the date it was written, and anyassumptions made by the programmer. This is not required but it isrecommended for good programming practice.
The symbols /* signify the start of the comment, while */ signify theend of the comment. A comment enclosed in /* */ can encompassmore than one line.
Example 1. /* Juan dela Cruz
* Last Modified : March 22, 1999
* The program will compute my GPA.
*/
Example 2. /* This formula computes the interest */
Header files
Header files are statements that tell the compiler what additionalfiles to process before processing the actual program. These files contain useful functions (subprograms) that have been pre-written.
Format:
#include <<header file>>
|
Example:
#include <stdio.h>
Constant Definition
Constants are defined for values which will not change throughoutthe entire program.
Format:
#define <constant identifier> <literal>
|
EXAMPLE:
#define SCHOOL “De La Salle University”
#define PI 3.1416
#define MID_INIT ‘T’
#define MAX_STUD 45
Main Program
This is the main section or the main block of the entire program. Itis the first part of the program to be executed.
Format:
main()
{/*variable declaration*/
/*statements*/}
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The open brace ({) signify the start of the program, while the(}) signify the end of the program. Within the braces, variabledeclarations should be made. The statements enclosed within thebraces form part of the main program.
Variable declaration
They are usually declared before the start of the program code. The
variable declarations tell C compiler what type of data will be stored
in each variable and how that data will be represented in memory.
Format:
<datatype> <variable list>;
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The type of data that can be stored in a variable are integer, real, and character. For integer, the keyword int is used to define the data type. On the other hand, float and double are used to define real values.
The char data type requires one byte of memory space and the range of
values that can be assumed is from 0 to 255. The number to character
coding that is used is ASCII. The amount of memory space required to
store an int, a float, and double is platform-dependent (depends on the
machine and the software).
Following ranges apply for Linux:
Data type
|
Range
| ||
Int
|
-2147483648 to + 2147483647
| ||
Long
|
-2147483648 to + 2147483647
| ||
Float
|
3.7e-38 to 3.4e38
| ||
Double
|
1.7e-308 to 1.7e308
| ||
Data type
|
Prefix
| ||
Int
|
n
| ||
Long
|
l
| ||
Float
|
f
| ||
Double
|
d
| ||
Char
|
c
| ||
Example:
Int nAge ;
Float fTotal ;
Double dAmount ;
Char cMenuOption ;
Assignment Statement
It stores a value or a computational result in a variable. They are
used commonly to perform most arithmetic operations in a program.
Format:
<variable> = <expression>;
|
The symbol = is the assignment operator, read as “becomes,” “gets,” or
“takes the value of” rather than “equals.” The variable before the
assignment operator is assigned the value of expression after it. the
expression can be a variable, a constant, a literal, or a valid C
expression.
Example 1:
X=1; /*x is assigned a numeric literal*/
fValue= PI; /*fValue is assigned the value of a constant, assuming PI
was defined to contain the constant 3.1416*/
chl=cLast; /*chl gets the value of a variable*/
Format:
<datatype> <variable> = <value>;
|
The value could either be a defined constant identifier or a literal.
Example 2:
Int nMiles = 2 ;
Float fVal1 = PI ; /*assume PI is a constant*/
Char cCh = `N´ ;
- As
mentioned before, a series of variables can be declared at the same
time. But, take note that if the declaration of a series of variables is
done together with the initialization, each variable have to
initialized separately.
Example 3. int x, y, z = 1;
In
the above example, although x, y, and z are declared as variables that
will contain integers, only z has been initialized with the value of 1.
Both x and y still contain garbage values. To initialize all the
variables, either assign each variable with a value or use successive
assignment operators.
Example4:
int x = 0, y = 1, z = 1;
The example shows that x is assigned with 0, while y and z are assigned with.
1. Supposing, we want to initialize x to 1 also, we might as well use successive assignment operators.
Example5:
Int x, y, z;
x = y = z = 1;
x = y = z = 1;
The
value is assigned from right to left. The variable z is assigned with 1
first, then the value of z will be given to y, and lastly, the value of
y will be given to x. Note that because of how the values are
initialized, we cannot write something like this:
int x = y = z = 1;
The following example shows that variables can also be assigned an expression.
Example6:
kms = KMS_PER_MILE * miles;
Before
the assignment operation is evaluated, the value of kms is unknown.
Assume that KMS_PER_MILE has a value of 1.6, and miles has a value of 2.
After the operation, kms would now have a value of 1.6 * 2 or 3.2.
One
should take note that the variable and expression must have the same
data type. Otherwise, the result of the expression will be converted to
the data type of the variable.
Example7:
Int kms;
kms = 1.6 * 2;
kms = 1.6 * 2;
As
seen in Example 6, the result of the expression would be 3.2. However,
since kms is declared as an integer, the fractional part is dropped. Therefore, the value of kms after the assignment operation is 3.
Example
7 can also be rewritten as int kms = 1.6 * 2; since we mentioned that
we can initialize a variable with a value while declaring it.
Example8:
sum = sum + 10;
If
you can notice, the same variable name appears both on the left and the
right side of the assignment operator. The statement instructs the
computer to add the current value of sum to 10, and the result is
assigned back to sum. Assume sum has an initial value of 100.
Before assignment: sum has the value 100
After assignment: sum has the value 100+10 or 110
Shortcuts on Assignment Statement
Increment and Decrement
The
statement i = i + 1; gets the value of i, adds it with 1, and stores it
again to i. As a result, if the initial value of i is 5, after
executing this statement, i will have the value of 6. To simplify the
increment statement, C allows us to use the increment and decrement
operators.
The increment operator ++ takes a single variable as its operand. The variable is only incremented by one.
i++;
The value of the expression in which the ++ operator is the value before it is incremented.
Example:
n = 4;
printf (“%d \n”, n++);
printf (“%d \n”, n);
Output:
4
5
C also provides a decrement operator, --. Its function is similar to the increment operator.
Other Assignment Operators
For
assignment statements that add more than 1, we can not use the
increment operator anymore. However, C provides some shortcut assignment
operators aside from =. These are the +=, -=, *=, /=, and %=.
Whenever we see the following format:
Before:
<variable> = <variable> <operator> <expr> ;
|
We can now use the shortcut assignment operator in the following format:
After:
<variable> <operator>= <expr>;
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Example:
I=i+2; is equivalent to i+=2;
X=x-15; is equivalent to x-=15;
Amt=amt*(1+rate);
is equal to amt*=1+rate;
Share=share/4; is equal to share/=4;
J=j%2; is equivalent to j %=2;
Input and Output Statements
The
functions scanf() and printf() are used for input and output,
respectively. (The f in printf and scanf stands for “formatted”.) These
functions exist in the standard input/output (stdio) library and are
available whenever a C system resides.
The printf Statement
Format:
Printf(<format string>[,<print list>]);
|
The printf() function has a format string and print list as its arguments. The simple statement
printf( “Let’s Eat!” );
prints
the words Let’s Eat on screen. To show the flexibility of the printf
function, let us show the different ways of printing the word Eat on
screen:
printf(“let’s Eat!”);
printf(“let’s %s!”, “eat”);
printf(“let’s %c%c%c!”, ‘E’, ‘a’, ‘t’);
Single
quotes are used to designate character literal. The format %c prints
the value of an expression as a character. Note, also, that any space in
the format string will be reflected on the screen output.
When
an argument is printed, the place where it is printed is called its
field and the number of characters in its field is called its field
width. The field width can be specified in a format as an integer
occurring between the % and the conversion character. This is discussed
in a short while.
The
expression in print list are evaluated and converted according to the
formats in the format string. The % symbol introduces a conversion
format. A single conversion format is a string that begins with % and
ends with a conversion character.
Conversion Character
|
How the corresponding argument is printed
|
C
|
as a character
|
D,I
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as a decimal integer
|
F
|
as a real number: example: 1.230000
|
S
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as a string
|
%
|
the % character is printed instead
|
The scanf statement
 |
The scanf() function is passed a list of arguments that can be treated asformatstring and input list. Its
first argument string having formats that correspond to the various way
the characters in the input stream are to be interpreted. It is merely a
string and may contain conversation specifications or formats - begins
with a % character and ends with a conversation character. The input lists are addresses where input values are stored.
When the user inputs values into a program, the sequence of characters (called input stream)
are received by the program. For example, if the user types in the
number 123, the program receives this as a sequence of characters. The
scanf() function can be used to convert a string of decimal digits into
an integer value and stores it at an appropriate place in the memory,
specified by input list.
Example 1.
Scanf( “%d”, &x ) ;
The formatted %d is matched with &x, causing the function to
interpret the sequence of characters input as a decimal integer and to
store the result as “the address if x”
Example 2.
Char a, b, c;
int n;
float x;
scanf ( “%c%c%c%d%f”, &a, &b, &n, &x ) ;
For the above example, we have the following format string“%c%c%c%d%f” , and the following input list:
&a, &b, &n, &x . The input list following the format
string consists of addresses separated by commas. It should be noted
that the conversion characters in the format string is not separated by
spaces.
The table below shows the table showing the commonly-used conversion characters.
Note that the scanf, the conversion character for double is lf, whereas in printf, the conversion character is f only.
Other Formatting
Explicit
formatting information may be included in a conversion specification of
printf statement. If it is not included, then defaults are used. For
example, the format %f with corresponding argument 3.77 will result in
3.770000 being printed. The number is printed with six digits to the
right of the decimal point by default.
Between the % symbol that starts the conversion specification and a
conversion character that ends it, there may appear (in order):
· zero or more flag characters, discussed below.
· an optional positive integer that
specifies the minimum field width of the converted argument. If the
converted argument has fewer characters than the specified field width,
then it will be padded with spaces on the left or right, depending on
whether the converted argument is left- or right-justified. Numbers are
right-justified, therefore the spaces are padded at the left. Similarly,
spaces for characters and strings are padded at the leftmost end. If
the converted argument has more characters than the specified field
width, then the field width will be extended to whatever is required. If
the integer defining the field width begins with a zero and the
argument being printed is right-justified in its field, then zeroes
rather than spaces will be used for padding.
· anoptional precision,
which is specified by a period (.) followed by a nonnegative integer.
For d and i conversions, it specifies the minimum number of digits to be
printed. For f conversions, it specifies the number of digits to the
right of the decimal point. For an s conversion, it specifies the
maximum number of characters to be printed from a string.
The flag characters are:
· a
minus sign, which means that the converted argument is to be
left-adjusted in its field. If there is no minus sign, then the
converted argument is to be right-adjusted in its field.
· a
plus sign, which means that a nonnegative number that comes from a
signed conversion is to have a + appended. All negative numbers
automatically start with a minus sign.
· a zero means that zeroes are used for padding, instead of spaces.
Example.
A C Program
Recall
that in Chapter 1, we formulated our algorithm to compute for the final
grade. Now that we have seen the different parts of a C program and we
have discussed some simple statements in C, let us now put it together.
/***********************************************
File Name :grade.c
Author :Nathatlie Rose Lim
Last Modified :April 25, 2002
This program computes the final grade.
***********************************************/
#include <stdio.h>
#define GREETING “Hello, Let’s compute your grade.”
main()
{
float fQ1, fQ2, fMp1, fMp2, fFE, fTE, fFG;
printf ( “%s\n” , GREETING) ;
/* get quiz grades from user */
printf(“Enter quiz 1: “);
scanf("%f", &fQ1);
printf(“Enter quiz 2: “);
scanf("%f", &fQ2);
/* get project grades from user */
printf(“Enter project 1: “);
scanf("%f", &fMp1);
printf(“Enter project 2: “);
scanf("%f", &fMp2);
/* get final exam grade from user */
printf(“Enter final exam: “);
scanf("%f", &fFE);
/* get teacher’s eval from user */
printf(“Enter teacher’s evaluation: “);
scanf("%f", &fTE);
/* compute final grade */
fFG = 0.50 * ((fQ1 + fQ2)/2) +
0.15 * ((fMp1 + fMp2)/2) +
0.3 * fFE + 0.05 * fTE;
printf("\nThe Final Grade = %.2f\n", fFG);
}
Frequently Asked Questions
1.What is a statement?
All
C programs are made up of a sequence of instructions. In Cinstructions
are also called statements. In the English language, a statement is
terminated by a period, a question mark, or an exclamation point. In C, a
statement is terminated by a semicolon.
2.What is the use of { } symbols?
The
symbol { and } are called open and close brace, respectively. They
signify the start and the end of a block. Note that the braces always
come in pairs.
3. What is the use of /* */ symbols?
These
symbols group comments inside the program. Comments are not
instructions, rather they simply provide additional information (a
textual description) such as what the program is doing, what are the
inputs and outputs, etc. Comments are optional and may be placed
anywhere within the program source code.
4. What is a variable?
A
variable is an entity that is used to store data. It is the name that
the programmer uses to indicate what space in the memory he wants to
access. For this space to be accessed, it should be reserved first.
Reserving a memory space and giving it a name is called variable
declaration. The type of data (data type) to be stored in the memory
will indicate how much space is going to be reserved. Each variable has a
name, an associated physical memory space (in RAM), a data type, a
value, a scope, and a lifetime.
5. What is a data type?
A data type specifies :
· the kind of values that can be assumed by a variable of that type
· the range of values that can be assumed by a variable of that type
· the amount of memory (in bytes) needed by a variable to store a value of that type
6.Can I use any name for the variables?
Yes,
as long as you follow the naming conventions, and do not use the
reserved words in C. It is recommended, however, as a good programming
practice, for you to use a name that is descriptive or suggestive. Refer
to Appendix C to make the format of your variables more readable.
7. What is the value of the variable initially?
By
default, the value of a variable is garbage, i.e., there is something
stored in that memory space but that something is invalid for the
intended use. Using variables with garbage values will cause logical
errors.
8. What will happen if I assigned a value whose data type is different from the data type of the receiving variable?
The
value will be converted. In general, one that requires smaller memory
will fit into the variable with a larger space. The opposite will result
to loss of information (which could cause a logical error). The basic
rules of data type conversion are as follows:
· int to float/double : value will be converted to floating-point value
· float/double to int : the fractional part is dropped
· char
to int/float/double : the char value (based from ASCII character set)
will be converted automatically to int/float/double with no problem
· int
to char : if the int value is within the possible range of char values
(0 – 255) then that value is assigned and converted to the ASCII
character equivalent; otherwise, the value assigned could be
unpredictable
· float/double
to char : the fractional part will be discarded and with the whole
number part, the same rule as int to char will be applied
9. Does the C language include commands for input/output?
No.
Actually, the C programming language by itself does not include
commands for input/output of data. However, there is a predefined
standard input/output library that can be linked with the programmer’s
object file. That is the reason why we need to include stdio.h.
Common Programming Errors
1. Assigning a variable to a literal is an error. For this reason, it is an error to write
123 = a
2. Assigning
the value of a variable of the same name is syntactically correct, but
is useless and actually does not make sense. For example:
int a;
a = 10;
a = a;
3. The
logical operator and should be &&, not &. The logical
operator or should be ||, not |. Using & and | will not result to a
syntax error, but will cause a logical error.
4. In
defining a constant, you do not need to use the assignment operator, =,
nor end the statement with a semicolon (;). Thus, the following is
incorrect
#define PI = 3.1416;
5. A
character literal is enclosed in a pair of single quotes. To represent
null character, you have to use ‘\0’. It is wrong to have a pair of
single quotes containing nothing. Therefore, do not write
charch;
ch = ‘’;
6. It is incorrect to omit the format string in a printf or scanf statement. For this reason, it is wrong to write
intnValue;
scanf(nValue );
printf(nValue );
7. There
should be an ampersand (&) sign before a variable when used as an
input variable. This specifies the memory location where the input will
be stored. Thus, it is wrong to write
intnValue;
scanf( “%d”, nValue );
8. The
number of input variables should correspond to the number of conversion
specification. The following statements will produce unpredictable
results.
int nValue1, nValue2;
scanf( “%d%d”, &nValue1 );
scanf( “%d”, &nValue1, &nValue2 );
printf( “%d%d”, nValue1 );
printf( “%d”, nValue1, nValue2 );
9. A
variable declared to contain a double value should use %lf as the
conversion character in a scanf statement. However, the conversion
character should be %f in a printf statement, whether a variable is
declared as a float or double. Thus, incorrect results will occur if you
write:
doubledTotal;
scanf( “%f”, &dTotal );
printf( “%lf”, dTotal );
10. String
literals are enclosed in a pair of double quotes (“). String literal
cannot span more than one line. Thus, it is incorrect to write
printf( “Hello
World” );
Self Evaluation Exercises
1. Write a program that inputs a 3-digit number and then display each of the digits.
2. Write
a program that asks the user to enter the radius of a circle and then
computes for its area. Recall that the formula to compute for the area
is AREA = 3.1416 * where R2 is the radius. The output of the
program must be similar to the one below. The area of the circle with
radius 2 cm. is 12.56 sq. cm.
3. Write a program that will ask the user that asks for a distance in kilometers and converts it to its metric equivalent.
4. Write a program that inputs two real numbers then exchange their values.
5. Workers
at a particular company were given a 15.5% salary increase. Moreover,
the increase was effective 2 months ago. Write a program that takes the
employee’s old salary as input and output the amount of retroactive pay
(the increase that wasn’t given for the past 2 months) and the
employee’s new salary.
Chapter Exercises
1. Create a program that will get as input from the user the base and the height of a triangle. Compute the area of the triangle.
Example Run:
Enter base: 15
Enter height : 3
The area of the triangle is 22.5
2. Create a program that converts a Fahrenheit measure to a Celsius measure (C = 5/9 x (F – 32)).
3. Philippine
currency is broken down into 1000, 500, 200, 100, 50, 20, and 10 peso
bills, and 5 and 1 peso coins. Write a program that would input an
integer amount in pesos and output the smallest number of bills and
coins that would add up to thatamount.
4. Write a program that displays the reverse of an input 3-digit number while retaining it as a whole.
5. Ten
young men agreed to purchase a gift worth Php10,000 for their boss. In
addition, they agreed to continue their plan even if at least one of
them dropped out. Write a program that would input the number of men who
dropped out (assume 0 to 9 only) and output how much more will each
have to contribute toward the purchase of the gift. The display should
the format in the sample run below:
Example Run:
Enter number of persons who dropped out: 3
Original contribution per person: Php1000.00
Additional contribution per person: Php428.57
Computed contribution per person: Php1428.57
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