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CHAPTER 4: The Basic of C
CSEB113 PRINCIPLES of PROGRAMMING CSEB134
PROGRAMMING I
byBadariah Solemon
1BS (May 2012)
Topics1. C Tokens2. Basic Data Types3. Variables4. Constants5. Reading Data from the Keyboard6. Arithmetic Operators and Expressions7. Single Character Data
2BS (May 2012)
C TOKENS
Topic 1
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Tokens & Types of Tokens• Token – the basic element on a C program recognized by the
compiler
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/* Example Case: ApplesAuthor: Mdm Badariah Solemon*/#include <stdio.h>int main(){
int Qty;double Cost=0.0, Total=0.0;
printf ("Enter quantity of apples purchased (in Kg):");scanf("%d", &Qty);
printf ("Enter the cost per Kg of apples (in RM per Kg):");scanf("%lf",&Cost);
Total = Cost * Qty;
printf("\nTotal cost of apples = %.2f\n",Total);
return 0;}
/* Example Case: ApplesAuthor: Mdm Badariah Solemon*/#include <stdio.h>int main(){
int Qty;double Cost=0.0, Total=0.0;
printf ("Enter quantity of apples purchased (in Kg):");scanf("%d", &Qty);
printf ("Enter the cost per Kg of apples (in RM per Kg):");scanf("%lf",&Cost);
Total = Cost * Qty;
printf("\nTotal cost of apples = %.2f\n",Total);
return 0;}
identifiersstring literals
reserved words
punctuation
operator
1. Reserved Words• Keywords that identify language entities such
as statements, data types, language attributes, etc.
• Have special meaning to the compiler, cannot be used as identifiers in our program.
• Should be typed in lowercase.• MUST NOT be used as identifiers!!• Ex: auto, double, else, void, i
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Task: Identify the KeywordsData Type-related Flow of Control-related Miscellaneous
int if enum
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2. Identifiers• Words used to represent and reference
certain program entities (variables, constant, function names, etc).
• Also known as programmer-defined words.• Example:
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int myName; myName is program
variable.
int myName; myName is program
variable.
void CalculateTotal(int value); CalculateTotal is a function
name.
void CalculateTotal(int value); CalculateTotal is a function
name.
#define TAXRATE 26 TAXRATE is a
constant.
#define TAXRATE 26 TAXRATE is a
constant.
Identifiers: Rules
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Rules Example
Can contain a mix of characters and numbers. However it cannot start with a number
H2o
First character must be a letter or underscore Number1; _area Can be of mixed cases including underscore character
XsquAre my_num
Cannot contain any arithmetic operators R*S+T
… or any other punctuation marks… #@x%!!
Cannot be a C keyword/reserved word struct; printf;
Cannot contain a space My height
… identifiers are case sensitive Tax
TaX
TAX are different
Identifiers: Naming Styles• Avoid excessively short and cryptic names
such as x, or wt. • Use reasonably descriptive name such as student_name and StudentID.
• Use userscores or capital letters to separate words in identifiers that consist of two or more words.– Example: StudentName, student_name, or studentname
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3. String Literals• A sequence of any number of characters surrounded
by double quotation marks “ ”. • Example:
• Example of usage in C program:
Produces output:
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“This is a string constant.”“Hello \”John”\.”“This is a string constant.”“Hello \”John”\.”
printf(“My name is David Beckham.\n”);printf(“My name is David Beckham.\n”);
My name is David Beckham.My name is David Beckham.
4. Operators• Tokens that result in some kind of
computation or action when applied to variables or other elements in an expression.
• Example of operators:* + = - / < >
• Usage example:result = total1 + total2;
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5. Punctuators• Symbols used to separate different parts of the C
program.• These punctuators include:
[ ] ( ) { } , ; “: * #
• Usage example:
– To be discussed when we come to the proper language feature in the coming chapters.
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main(){
printf(“Testing.”);}
main(){
printf(“Testing.”);}
Exercise1. Valid/invalid – variables or constant
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Variables/ Constant
Valid/ Invalid?
Variable/ Constant
Valid/ Invalid?
CO2 const
_prs Formula #1
2ndDay Last.Name
First_name account#
NetPRIce engine 1
my name main
index Main
m*cee First+Last
mx_2ndcoverage typedef
BASIC DATA TYPES
Topic 2
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Basic Data Typesint
Whole numbers, positive and negativeEx:
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double
To declare floating point variable of higher precision or higher range of numbers - exponential numbers, positive and negativeEx:
float
Fractional parts, positive and negativeEx:
char*
Single character:1.Numeric digits: 0 - 92.Lowercase/uppercase letters: a - z and A - Z3.White space4.Special characters: , . ; ? “ / ( ) [ ] { } * & % ^ < > Ex:
double bigvalue = 12E-3;//equals to 12x10-3
char initial = ‘B’;
int number = 12;int sum = -3678;
float short = 0.000983;float income = 1234567890.12;
VARIABLES
Topic 3
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What are Variables?• Are memory locations within the computer which
allows pieces of data to be stored.• The word variable comes from the word vary, which
means that whatever you place within a variable can be changed.
• A variable can be viewed as a container used to store things (numbers, character, string etc )
• Types of operations:1. Declaring variables names2. Assigning variable values 3. Manipulating variable values
– ex: display on the screen
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Declaring Variables• A variable is declared by specifying the DATA
TYPE of the variable name• Ex:
• Several variables of the same data type may be declared in the same statement.
• Ex:
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int Age;int Age;
Variable NameData Type
int Age, Weight;int Age, Weight;
Variable NamesData Type
Comma to separate variables
Assigning Values to Variable• A variable is assigned with a value using an
assignment operator =.• Ex:
• During program execution, may be conceptually viewed as:
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Variable Name Data Type Data Value Memory Cell Address*
Age int 17 ffff8
Weight int 60 ffff2
Age = 17;Age = 17;
17 is assigned to Age
Weight = 60;Weight = 60;
60 is assigned to Weight
Assigning Values to Variables During Declaration
• Variables may be assigned with values even during the variables declaration.
• Ex:
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int Age = 17, Weight = 60;int Age = 17, Weight = 60;
Data Type
Comma to separate variables
int Age = 17;int Age = 17;
Variable Name
Printing Variable Values• Use the printf() function to display the value of a variable
on the computer screen.• Syntax:
• FormatString is a combination of characters, placeholders and escape sequence.
• PrintList is any constants, variables, expressions, and functions calls separated by commas.
• Example:
BS (Feb 2012) 21
printf(FormatString, PrintList);
int age = 80;float cgpa = 4.00;printf(“Your age: %d\n”, age);printf(“CGPA: %f\n”, cgpa);printf(“My CGPA: %.2f\n”, cgpa);
int age = 80;float cgpa = 4.00;printf(“Your age: %d\n”, age);printf(“CGPA: %f\n”, cgpa);printf(“My CGPA: %.2f\n”, cgpa);
placeholder
Your age: 80CGPA: 4.000000My CGPA: 4.00
Your age: 80CGPA: 4.000000My CGPA: 4.00
Placeholders in printf() Function
• Placeholders (or also known as format specifiers) always begin with the symbol %
• Are used to format and display the variable/constant values on the screen
• Common placeholders:
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Placeholder Data Type
%d int
%f double/float
%c char
%s String
Refer Table 12.2, pg 647 (Hanly & Koffman)
More About Printing Variable Values
• Recall this syntax:
– FormatString can have multiple placeholders if the Printlist in printf() function has several variables.
• Example:
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#include <stdio.h>main(){
int age = 80;float cgpa = 3.512, weight = 60.4778;
printf(“Age: %d and CGPA: %.2f\n”, age, cgpa);printf(“CGPA: %.2f and Age: %d\n”, cgpa, age);printf(“CGPA: %.1f\tWeight2: %.2f\n”, cgpa, weight);printf(“Weight3: %.3f\t”, weight);printf(“Weight4: %.4f\n”, weight);
}
#include <stdio.h>main(){
int age = 80;float cgpa = 3.512, weight = 60.4778;
printf(“Age: %d and CGPA: %.2f\n”, age, cgpa);printf(“CGPA: %.2f and Age: %d\n”, cgpa, age);printf(“CGPA: %.1f\tWeight2: %.2f\n”, cgpa, weight);printf(“Weight3: %.3f\t”, weight);printf(“Weight4: %.4f\n”, weight);
}
printf(FormatString, PrintList);
Exercise • Do hand-out exercise – declare & assign variables
• What happen if you try to print an int with %f or a float with %d?
• What is the output for the following program?
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#include <stdio.h>main(){
int yearS = 4;float cgpa = 3.88, gpa = 4.00;double
printf(“How long it takes to complete ur study?\n%d\n”,yearS);printf(“GPA\t\tCGPA\n”);printf(“%.2f\t\t%.2f”,gpa, cgpa);printf(“Excellent!\n”);printf(“Now, test your skill\n”);printf(“CGPA in 1 decimal point = %.1f\n”, cgpa);printf(“CGPA = %f\n”, cgpa)}
#include <stdio.h>main(){
int yearS = 4;float cgpa = 3.88, gpa = 4.00;double
printf(“How long it takes to complete ur study?\n%d\n”,yearS);printf(“GPA\t\tCGPA\n”);printf(“%.2f\t\t%.2f”,gpa, cgpa);printf(“Excellent!\n”);printf(“Now, test your skill\n”);printf(“CGPA in 1 decimal point = %.1f\n”, cgpa);printf(“CGPA = %f\n”, cgpa)}
CONSTANTS
Topic 4
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Constants• Entities that appear in the program code as
fixed values.• Types of operations:
1. Declaring and assigning constant values2. Operating constant values
— Almost similar treatment like variables but CANNOT change the values after declaration!
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Declaring Constants1. As constant macro – created using a
preprocessor directives using define keyword – Ex:
2. Within a function using the const keyword.– Ex:
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#include <stdio.h>#define PI 3.14159#define DAYS_IN_YEARS 365 main(){ …
#include <stdio.h>#define PI 3.14159#define DAYS_IN_YEARS 365 main(){ …
#include <stdio.h>main(){ const double KMS_PER_MILES = 1.609 …}
#include <stdio.h>main(){ const double KMS_PER_MILES = 1.609 …}
DATA TYPE?
Types of ConstantsInteger Constant
Positive or negative whole numbers Ex:
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Character Constant
A character enclosed in a single quotation markEx:
Floating-point Constant
Positive or negative decimal numbers Ex:
Enumeration
Values are given as a listEx:
#define LETTER ‘n’const char NUMBER = ‘1’;
enum Language { English Arabic Mandarin}
#define MAX 10const int MIN = -90;
#define PI 3.412const float PI = 3.412;#define VAL 0.5877e2const double VAL = 0.5877e2; //stands for 0.5877 x 102
Printing Constant Values• Similar to printing variable values
– What is the output of the program?
BS (Feb 2012) 29
#include <stdio.h>
#define DAYS 365
#define VAL 0.5877
void main(void)
{
const double PI = 3.412;
printf(“pi = %.3f\n”, PI);
printf(“In a year, there are %d days\n”, DAYS);
printf(“Value = %.4f\n”, VAL);
}
#include <stdio.h>
#define DAYS 365
#define VAL 0.5877
void main(void)
{
const double PI = 3.412;
printf(“pi = %.3f\n”, PI);
printf(“In a year, there are %d days\n”, DAYS);
printf(“Value = %.4f\n”, VAL);
}
READING DATA FROM THE KEYBOARD
Topic 6
BS (May 2012) 30
Using scanf() Function• To read data from the standard input device (usually
keyboard) and store it in a variable.• The general format is pretty much the same as printf() function.
• Syntax:
• InputList one or more variables addresses, each corresponding to a placeholder in the FormatString
• One placeholder for each variable in InputList.• The two or more variables in InputList must be separated by
commas.• Each element of InputList must be an address of a memory
cell(using prefix & address operator)
BS (Feb 2012) 31
scanf(FormatString, InputList);
Placeholders in scanf() Function
• Are used to format and display the variable/constant values keyed-in by the user
• Common placeholders in scanf() function are very similar to placeholders in printf() function:
BS (Feb 2012) 32
Placeholder Data Type
%d int
%f float
%lf double
%c char
%s String
Refer Table 12.2, pg 647 (Hanly & Koffman)
Example
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Address operator
int Age;double income;
printf(“Enter your age and income“);scanf(“%d %lf”, &Age, &income);
printf(“Your age: %d\n”, Age);printf(“Your income: %f\n”, income);
int Age;double income;
printf(“Enter your age and income“);scanf(“%d %lf”, &Age, &income);
printf(“Your age: %d\n”, Age);printf(“Your income: %f\n”, income);
int Age; float income;
printf(“Enter your age: “);scanf(“%d”, &Age);
printf(“Enter income: “); scanf(“%f”, &income);
printf(“Your age is: %d\nIncome: %.2f”, Age, income);
int Age; float income;
printf(“Enter your age: “);scanf(“%d”, &Age);
printf(“Enter income: “); scanf(“%f”, &income);
printf(“Your age is: %d\nIncome: %.2f”, Age, income);
If you want the user to enter more than one value, you serialise the inputs.
Exercise
• Write a simple C program that read two integer values and print them on the screen in one same line separated by one vertical tab. Follow this sample output:
• Write another simple C program that read 3 real numbers and print them on the screen in reverse order. Follow this sample output:
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Enter first integer: 80Enter second integer: 9980 99
Enter first integer: 80Enter second integer: 9980 99
Enter three real numbers: 5.6 7.8 9.3
In reverse order: 9.3 7.8 5.6
Enter three real numbers: 5.6 7.8 9.3
In reverse order: 9.3 7.8 5.6
ARITHMETIC OPERATORS AND EXPRESSIONS
Topic 5
BS (May 2012) 35
Arithmetic Expressions• A syntactically correct and meaningful combination
of operators and operands is known as an Expression.
• ‘=’ is the basic assignment operator• Syntax:
• Example:
BS (May 2012) 36
cityTax = CITYTAXRATE * grossIncome; cityTax = CITYTAXRATE * grossIncome;
Variable = ArithmeticExpression;
assignment operator arithmetic operator
operands
Expression:
month = 12; month = 12;
12 is assigned to variable month
Arithmetic Operators• There are 2 types of arithmetic operators in C:
1. Unary operators are operators that require only one operand.• Example:
2. Binary operators are operators that require two operands.• Example:
• Note that we CANNOT write arithmetic expressions like the following:
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operand
second = -first;prs = -34;second = -first;prs = -34;
third = first / second;sum = 30 + 76;third = first / second;sum = 30 + 76;
operands
first / second = third;30 + 76 = sum;first / second = third;30 + 76 = sum;
XX
1. Unary Operators
• Initial value of a is 10 and b is 5
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prefix (before a variable)
postfix (after a variable)
Prefix/Postfix Increment• a++ or ++a is equals to a = a + 1 but they work
differently
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Prefix Increment (++a) Postfix Increment (a++)1. Add the value of a by 12. Return the value a
1. Return the value a2. Add the value of a by 1
Example:int a=9;
printf(“%d\n”, a);
printf(“%d\n”, ++a);
printf(“%d”, a);
Output:9
10
10
Example:int a=9;
printf(“%d\n”, a);
printf(“%d\n”, a++);
printf(“%d”, a);
Output:9
9
10
Prefix/Postfix Decrement• Similarly, --a or a-- is equals to a = a - 1 but they
work differently
BS (May 2012) 40
Prefix Decrement (--a) Postfix Decrement (a--)
1. Subtract the value of a by 12. Return the value a
1. Return the value a2. Subtract the value of a by 1
Example:int a=9
printf(“%d\n”, a);
printf(“%d\n”, --a);
printf(“%d”, a);
Output:988
Example: int a=9; printf(“%d\n”, a);
printf(“%d\n”, a--);
printf(“%d”, a);
Output:998
2. Binary Operators• If all operands in an arithmetic expression are of type double/float, the result is also of type double/float except for modulus
operator. • If all operands in an arithmetic expression are of type int, the result is also of type int.
• Value of a is 9
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Modulus Operator (%)• You could only use modulus (%) operation on
integer variables/integer division• Modulus will result in the remainder of an
operation• Example:
– 7 % 2 is 1
– But 2 % 7 is 2. Any idea why?
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72
3
6
1
-
7/2
7%2
integral
remainder
Example• A simple C program that find an average of
two real numbers.
BS (May 2012) 43
#include <stdio.h>
void main(void)
{
float no1, no2, sum, avg;
printf(“Enter three real numbers: “);
scanf(“%f %f”, &no1, &no2);
sum = no1 + no2;
avg = sum / 2;
printf(“Average: %.2f”, avg);
}
#include <stdio.h>
void main(void)
{
float no1, no2, sum, avg;
printf(“Enter three real numbers: “);
scanf(“%f %f”, &no1, &no2);
sum = no1 + no2;
avg = sum / 2;
printf(“Average: %.2f”, avg);
}
Exercise• Write a simple C program that sum up 4
integer numbers and display the computed sum.
• Covert the pseudocode/flowchart prepared to solve the following problems (refer slide 39 in Chapter 2) into complete C programs that:1. compute and display the average of three
numbers.2. read the value of the height, width and length of
a box from the user and print its volume.
BS (May 2012) 44
Compound Assignment Operator
• Are combinations operators with the basic assignment operator =
• Initial value of a is 8:
BS (May 2012) 45
Exercise• What is the output of the following
program?
BS (May 2012) 46
#include <stdio.h>
void main(void)
{
int first;
printf("Enter a value: ");
scanf("%d", &first);
printf("\nNew value is: %d\n\n", first+=4);
printf("\nNew value is: %d\n\n", first*=4);
printf("\nNew value is: %d\n\n", first-=4);
printf("\nNew value is: %d\n\n", first%=4);
}
#include <stdio.h>
void main(void)
{
int first;
printf("Enter a value: ");
scanf("%d", &first);
printf("\nNew value is: %d\n\n", first+=4);
printf("\nNew value is: %d\n\n", first*=4);
printf("\nNew value is: %d\n\n", first-=4);
printf("\nNew value is: %d\n\n", first%=4);
}
Operations of Mixed or Same Types
BS (May 2012) 47
int
int
float
float
float
int
int
float
float
Examples:5 + 3 is 85/3 is 1 WHY?
5.2 + 3.1 is 8.35.0/3.0 is 1.6
5.2 + 3 is 8.25.0/3 is 1.65/3.0 is 1.6
Operations of Mixed or Same Types
BS (May 2012) 48
int
float
int
float
int/int int5/3 is 1
int/float float 5/3 is 1.6
m is 1
p is 1.0
n is 1
q is 1.6
Type Casting• You can modify the way C uses types in arithmetic operations
by using cast operators. The syntax:
• Recall:
• So what can you do to ensure that the operation produces 1.6 instead of 1?
• To ensure that you did not loose any data from the operation, you may apply type casting as follows:
BS (May 2012) 49
(type) expression
5/3 result in 15/3 result in 1
•(float)5/3•5/(float)3•(float)5/(float)3•((float)5)/((float)3)
•(float)5/3•5/(float)3•(float)5/(float)3•((float)5)/((float)3)
Guidelines in Writing Arithmetic Expressions
• If it is division operation, make sure it does not involve two integer variables or constants (unless you want the fractional part to be cut off)
• When writing your code, a float type variable is on the left side of an assignment statement. Example:
• When int type variable is on the left side of an assignment statement, make sure that the statement is meant to create an integer value.
BS (May 2012) 50
int sum = 87;float avg;
avg = sum / 4;
int sum = 87;float avg;
avg = sum / 4;
C Rules for Evaluating Expressions
• We must know the C rules for evaluating expression when there is multiple mix of operators in the expression.
• In this example, which operator should be evaluated first?
• The rules for evaluating expressions are:1. Parentheses rule: all expressions in () must be evaluated
separately. Nested parentheses – innermost first . Parentheses can be used to control the order of operator evaluation
2. Precedence rule: specifies which of the operators will be evaluated first.
3. Associativity rule: specifies which of the multiple occurrences of the same operators will be evaluated first.
BS (May 2012) 51
s = x / y + zs = x / y + z
Precedence and Associativity of Operations
• For details, refer to Appendix C (Hanly &Koffman)
• L – from left to right R – from right to left
BS (May 2012) 52
Precedence Operation Associativity
Highest (evaluated first)
Lowest (evaluated last)
[ ] ( )
postfix++ postfix--
prefix++ prefix-- unary+ unary- unary& unary*
* / %
binary+ binary-
= += -= *= /= %=
L
L
R
L
L
R
Example 1
The order: Evaluation steps (assume initial value of s is 2, x is 9, y is 1, z = 2):
Step 1: s = 9 / 1 + zStep 2: s = 9 + 2Step 3: s = 11
BS (May 2012) 53
s = x / y + zs = x / y + z
13 2
The order: Evaluation steps (assume initial value of i is 1, j is 7):
Step 1: i += 7 - 2Step 2: i = 6 (i += 5 i = 1 + 5)
i += j – 2i += j – 2
12 Other option?Use parentheses
Example 2
Note:– The expression inside a parentheses will be evaluated first.– The associativity rule of parentheses is left to right
BS (May 2012) 54
The order: Evaluation steps (assume initial value of p1 is 4.5, p2 is 9.0, t1 is 0.0, t2
is 60.0):
Step 1: v = (9.0 – 4.5) / (t2 – t1)Step 2: v = 4.5 / (60.0 – 0.0)Step 3: v = 4.5 / 60.0Step 4: v = 0.075
v = (p2 – p1) / (t2 – t1)v = (p2 – p1) / (t2 – t1)
1 3 24
Exercise 1 • Find output of the program fragment
BS (May 2012) 55
...int i=5, c=10, x;
x = +i++;printf("a) x = %d, i = %d\n", x, i);
x = ++x;printf("b) x = %d, i = %d\n", x, i);
x = c++ + i;printf("c) x = %d, i = %d\n", x, i);
x = --c + --i;printf("d) x = %d, i = %d\n", x, i);
x = i + -x;printf("e) x = %d, i = %d\n", x, i);...
...int i=5, c=10, x;
x = +i++;printf("a) x = %d, i = %d\n", x, i);
x = ++x;printf("b) x = %d, i = %d\n", x, i);
x = c++ + i;printf("c) x = %d, i = %d\n", x, i);
x = --c + --i;printf("d) x = %d, i = %d\n", x, i);
x = i + -x;printf("e) x = %d, i = %d\n", x, i);...
Exercise 2• Find output of the program fragment
BS (May 2012) 56
...int x, y=5,z=10, s=3, p, q, r;
x = z/3 + -y;printf("%d\n", x);
x = (x % 2) + (y – 3));printf("%d\n", x);
x = ++z + z * 2;printf("%d\n", x);
p = y * z – s + x / z;q = y * (z – s) + x / z;r = y * z – s + x / z;printf(“%d\n”, x);
...
...int x, y=5,z=10, s=3, p, q, r;
x = z/3 + -y;printf("%d\n", x);
x = (x % 2) + (y – 3));printf("%d\n", x);
x = ++z + z * 2;printf("%d\n", x);
p = y * z – s + x / z;q = y * (z – s) + x / z;r = y * z – s + x / z;printf(“%d\n”, x);
...
SINGLE CHARACTER DATA
Topic 7
BS (May 2012) 57
The Set of C Characters• The characters that can be used to form words,
number and expressions (depend upon the computer on which
the program is run).• Are grouped into 4 categories:
BS (May 2012) 58
Letters
•Uppercase A to Z•Lowercase a to z
White Space
• Blank space• Horizontal tab (\t)• Carriage return (r)
• New line (\n)• Form feed (\)
Digits
•0 to 9
Special Characters
See next page
C Special Characters
BS (May 2012) 59
Working with char Data Type
• Declaring character variables. Example:
• Assigning a character constant to character variables. Example:
• Using printf() function to print characters. Example:
• Using scanf() function to input characters. Example:
BS (May 2012) 60
char c1;char c2, c3, c4;char c1;char c2, c3, c4;
c1 = ‘p’;c2 = ‘\n’;c3 = ‘#’;
c1 = ‘p’;c2 = ‘\n’;c3 = ‘#’;
printf(“%c\n”, c1);printf(“%c %c”, c1, c2);printf(“%c\n”, c1);printf(“%c %c”, c1, c2);
scanf(“%c %c ”, &c1, c2);scanf(“%c%c”, &c3, &c4);scanf(“%c %c ”, &c1, c2);scanf(“%c%c”, &c3, &c4);
Each character is enclosed in single quotes ‘ ’
No spaces in the string literal
Character Input Output Functions
• getchar() – to read a character from standard input• putchar() – to write a character to standard output• Example:
• To be discussed further in Chapter 8: Characters and Strings
BS (Feb 2012) 61
#include <stdio.h>main(){
char myC;printf(“Please type a character: “);myC = getchar();printf(“\nYou have typed this character:
“);putchar(myC);printf(“\n”);
}
#include <stdio.h>main(){
char myC;printf(“Please type a character: “);myC = getchar();printf(“\nYou have typed this character:
“);putchar(myC);printf(“\n”);
}
Input Buffer & Flushing the Buffer
• The getchar() function works with the input buffer to get the information typed at the keyboard. – Buffer – a portion of memory reserved for temporarily holding
information that is being transferred.
• When getchar()function is used, it is easy to see an execution that is different than it should be.
• So, what you can do is to flush or empty the input buffer by using fflush (stdin); statement.
• Example:
BS (May 2012) 62
char c1, c2;printf(“Enter 2 characters:”);fflush(stdin);c1 = getchar();c2 = getchar();fflush(stdin);
char c1, c2;printf(“Enter 2 characters:”);fflush(stdin);c1 = getchar();c2 = getchar();fflush(stdin);
Summary• Basic elements (tokens) in C: reserved words,
identifiers, string literals, operators, punctuators• Working with variables and constants of types int, float, double, char
• Reading data using scanf() function• The C rules when evaluating expression with multiple
mix of operators in arithmetic expression:– Parentheses rule, precedence rule & associativity rule
• Pre/post fix - effects the result of statement• Working with single character data including
getchar() and putchar() functionsBS (May 2012) 63
