FOCP - INTRODUCTION TO C (Unit 4)–16marks with answers

FUNDAMENTALS OF COMPUTING & COMPUTER PROGRAMMING

UNIT IV – 16 Marks

INTRODUCTION TO C

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1. Explain in detail about ‘C’ declarations and variables.

In C, lowercase and uppercase characters are very important. All commands in C

must be lowercase. The C programs starting point is identified by the word main( ). This informs the computer as to where the program actually starts.

The brackets that follow the keyword main indicate that there are no arguments supplied to this program.

The two braces, { and }, signify the begin and end segments of the program. The purpose of the statement

include <stdio.h> is to allow the use of the printf statement to provide program

output. Text to be displayed by printf() must be enclosed in double quotes. The program has only one statement printf("Programming in C is easy.\n");

printf() is actually a function (procedure) in C that is used for printing variables and text. Where text appears in double quotes "", it is printed without modification. There are some exceptions however. This has to do with the \ and % characters. These characters are modifier’s, and for the present the \ followed by the n character represents a newline character. Thus the program prints

Programming in C is easy.

and the cursor is set to the beginning of the next line. As we shall see later on, what follows the \ character will determine what is printed, ie, a tab, clear screen, clear line etc. Another important thing to remember is that all C statements are terminated by a semi-colon ;

General rules of ‘C’ language:

· program execution begins at main()

· keywords are written in lower-case

· statements are terminated with a semi-colon

· text strings are enclosed in double quotes

· C is case sensitive, use lower-case and try not to capitalize variable names

· \n means position the cursor on the beginning of the next line

· printf() can be used to display text to the screen

· The curly braces {} define the beginning and end of a program block.

BASIC STRUCTURE OF C PROGRAMS

C programs are essentially constructed in the following manner, as a number of well

defined sections.

/* HEADER SECTION */

/* Contains name, author, revision number*/

/* INCLUDE SECTION */

/* contains #include statements */

/* CONSTANTS AND TYPES SECTION */

/* contains types and #defines */

/* GLOBAL VARIABLES SECTION */

/* any global variables declared here */

/* FUNCTIONS SECTION */

/* user defined functions */

/* main() SECTION */

int main()

{

}

A Simple Program

The following program is written in the C programming language.

#include <stdio.h>

main()

{

printf(“Programming in C is easy.\n”); }

INITIALISING DATA VARIABLES AT DECLARATION TIME

In C, variables may be initialized with a value when they are declared. Consider

the following declaration, which declares an integer variable count which is initialized to

10. int count = 10;

SIMPLE ASSIGNMENT OF VALUES TO VARIABLES

The = operator is used to assign values to data variables. Consider the following statement, which assigns the value 32 an integer variable count, and the letter A to the character variable letter

count = 32;

letter = ‘A’

Variable Formatters

%d decimal integer

%c character

%s string or character array

%f float

%e double

HEADER FILES

Header files contain definitions of functions and variables which can be incorporated into any C program by using the pre-processor #include statement. Standard header files are provided with each compiler, and cover a range of areas, string handling, mathematical, data conversion, printing and reading of variables.

To use any of the standard functions, the appropriate header file should be

included. This is done at the beginning of the C source file. For example, to use the function printf() in a program, the line

#include <stdio.h> should be at the beginning of the source file, because the definition for printf() is found in the file stdio.h All header files have the extension .h and generally reside in the /include subdirectory.

#include <stdio.h>

#include “mydecls.h”

The use of angle brackets <> informs the compiler to search the compilers include directory for the specified file. The use of the double quotes “” around the filename inform the compiler to search in the current directory for the specified file.

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2. Explain in detail about the constants, expressions and statements in ‘C’.

1. Constants: (with examples)

1. Numeric constants

a. Integer Constants

b. Real Constants

2. Character constants

a. Single character Constants b. String Constants

2. Expressions:

An expression represents a single data item, such as number or a character. Logical conditions that are true or false are represented by expressions.

Example: a = p – q / 3 + r * 2 - 1

3. Statements

· Assignment Statements – Definition and examples

· Null Statements – Definition and examples

· Block of statements – Definition and examples

· Expression statements – Definition and examples

· Declaration statements – Definition and examples

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3. Discuss about the various data types in ‘C’. (MAY 2009)

The four basic data types are

a. INTEGER

These are whole numbers, both positive and negative. Unsigned integers

(positive values only) are supported. In addition, there are short and long integers.

The keyword used to define integers is, int

An example of an integer value is 32. An example of declaring an integer variable called sum is,

int sum;

sum = 20;

b. FLOATING POINT

These are numbers which contain fractional parts, both positive and negative. The keyword used to define float variables is,

float

An example of a float value is 34.12. An example of declaring a float variable

called money is,

float money;

money = 0.12;

c. DOUBLE

These are exponentional numbers, both positive and negative. The keyword used

to define double variables is, double

An example of a double value is 3.0E2. An example of declaring a double variable called big is,

double big;

big = 312E+7;

d. CHARACTER

These are single characters. The keyword used to define character variables is,

char

An example of a character value is the letter A. An example of declaring a character variable called letter is,

char letter;

letter = ‘A’;

Note the assignment of the character A to the variable letter is done by enclosing the value in single quotes.

#include < stdio.h >

main()

{

int sum;

float money; char letter; double pi;

sum = 10; /* assign integer value */ money = 2.21; /* assign float value */ letter = ‘A’; /* assign character value */ pi = 2.01E6; /* assign a double value */ printf(“value of sum = %d\n”, sum );

printf(“value of money = %f\n”, money ); printf(“value of letter = %c\n”, letter ); printf(“value of pi = %e\n”, pi );

}

Sample program output

value of sum = 10

value of money = 2.210000 value of letter = A

value of pi = 2.010000e+06

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4. Describe the various types of operators in ‘C’ language along with its priority.

An ex pr e s s I o n is a sequence of operators and operands that specifies computation of a value, or that designates an object or a function, or that generates side effects, or that performs a combination thereof.

1. ARITHMETIC OPERATORS:

The symbols of the arithmetic operators are:-

Example:

#include <stdio.h>

main()

{

int sum = 50; float modulus; modulus = sum % 10;

printf(“The %% of %d by 10 is %f\n”, sum, modulus);

}

PRE/POST INCREMENT/DECREMENT OPERATORS

PRE means do the operation first followed by any assignment operation. POST

means do the operation after any assignment operation. Consider the following statements ++count; /* PRE Increment, means add one to count */ count++; /* P OST Increment, means add one to count */

Example:

#include <stdio.h>

main()

{

int count = 0, loop;

loop = ++count; /* same as count = count + 1; loop = count; */

printf(“loop = %d, count = %d\n”, loop, count);

loop = count++; /* same as loop = count; count = count + 1; */

printf(“loop = %d, count = %d\n”, loop, count);

}

If the operator precedes (is on the left hand side) of the variable, the operation is performed first, so the statement

loop = ++count;

really means increment count first, then assign the new value of count to loop.

2. THE RELATIONAL OPERATORS

These allow the comparison of two or more variables.

= = equal to

! = not equal

< less than

< = less than or equal to

> greater than

> = greater than or equal to

Example:

#include <stdio.h>

main() /* Program introduces the for statement, counts to ten */

{

int count;

for( count = 1; count <= 10; count = count + 1 )

printf(“%d “, count );

printf(“\n”);

}

3. LOGICAL OPERATORS (AND, NOT, OR, EOR) Combining more than one condition

These allow the testing of more than one condition as part of selection

statements. The symbols are

LOGICAL AND &&

Logical and requires all conditions to evaluate as TRUE (non-zero).

LOGICAL OR ||

Logical or will be executed if any ONE of the conditions is TRUE (non-zero).

LOGICAL NOT !

logical not negates (changes from TRUE to FALSE, vsvs) a condition.

LOGICAL EOR ^

Logical eor will be excuted if either condition is TRUE, but NOT if they are all true.

The following program uses an if statement with logical AND to validate the users input to be in the range 1-10.

#include <stdio.h>

main()

{

int number;

int valid = 0;

while( valid == 0 ) {

printf(“Enter a number between 1 and 10 à”);

scanf(“%d”, &number);

if( (number < 1 ) || (number > 10) ){

printf(“Number is outside range 1-10. Please re-enter\n”);

valid = 0;

}

else

valid = 1;

}

printf(“The number is %d\n”, number );

} Example: NEGATION

#include <stdio.h>

main()

{

int flag = 0;

if( ! flag ) {

printf(“The flag is not set.\n”);

flag = ! flag;

}

printf(“The value of flag is %d\n”, flag);

}

Example:

Consider where a value is to be inputted from the user, and checked for validity to be within a certain range, lets say between the integer values 1 and 100.

#include <stdio.h>

main()

{

int number;

int valid = 0;

while( valid == 0 ) {

printf(“Enter a number between 1 and 100”);

scanf(“%d”, &number );

if( (number < 1) || (number > 100) ) printf(“Number is outside legal range\n”); else

valid = 1;

}

printf(“Number is %d\n”, number );

}

4. THE CONDITIONAL EXPRESSION OPERATOR or TERNARY OPERATOR

This conditional expression operator takes THREE operators. The two symbols used to denote this operator are the ? and the :. The first operand is placed before the ?, the second operand between the ? and the :, and the third after the :. The general format is,

condition ? expression1 : expression2.

If the result of condition is TRUE ( non-zero ), expression1 is evaluated and the

result of the evaluation becomes the result of the operation. If the condition is FALSE (zero), then expression2 is evaluated and its result becomes the result of the operation. An example will help,

s = ( x < 0 ) ? -1 : x * x; If x is less than zero then s = -1

If x is greater than zero then s = x * x

Example:

#include <stdio.h>

main()

{

int input;

printf(“I will tell you if the number is positive, negative or zero!”\n”);

printf(“please enter your number now-à”);

scanf(“%d”, &input );

(input < 0) ? printf(“negative\n”) : ((input > 0) ? printf(“positive\n”) :

printf(“zero\n”));

}

5. BIT OPERATIONS

C has the advantage of direct bit manipulation and the operations available are,

Example:

/* Example program illustrating << and >> */

#include <stdio.h>

main()

{

int n1 = 10, n2 = 20, I = 0;

I = n2 << 4; /* n2 shifted left four times */

printf(“%d\n”, i);

I = n1 >> 5; /* n1 shifted right five times */

printf(“%d\n”, i);

}

Example:

/* Example program using EOR operator */

#include <stdio.h>

main()

{

int value1 = 2, value2 = 4;

value1 ^= value2;

value2 ^= value1;

value1 ^= value2;

printf(“Value1 = %d, Value2 = %d\n”, value1, value2);

}

Example:

/* Example program using AND operator */

#include <stdio.h>

main()

{

int loop;

for( loop = ‘A’; loop <= ‘Z’; loop++ )

printf(“Loop = %c, AND 0xdf = %c\n”, loop, loop & 0xdf);

}

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5. Explain about the various decision making statements in ‘C’ language.

(JAN 2009/FEB2010)

1. IF STATEMENTS

DECISION MAKING

The if statements allows branching (decision making) depending upon the value or state of variables. This allows statements to be executed or skipped, depending upon decisions.

The basic format is,

if( expression )

program statement;

Example:

if( students < 65 )

++student_count;

In the above example, the variable student_count is incremented by one only if the value of the integer variable students is less than 65. The following program uses an if statement to validate the users input to be in the range 1-10.

#include <stdio.h>

main()

{

int number;

int valid = 0;

while( valid == 0 ) {

printf(“Enter a number between 1 and 10 à”);

scanf(“%d”, &number);

/* assume number is valid */

valid = 1;

if( number < 1 ) {

printf(“Number is below 1. Please re-enter\n”);

valid = 0;

}

if( number > 10 ) {

printf(“Number is above 10. Please re-enter\n”);

valid = 0;

}

}

printf(“The number is %d\n”, number );

}

2. IF ELSE

The general format for these are,

if( condition 1 )

statement1;

else if( condition 2 )

statement2;

else if( condition 3 )

statement3; else statement4;

The else clause allows action to be taken where the condition evaluates as false (zero). The following program uses an if else statement to validate the users input to be in the range 1-10.

Example:

#include <stdio.h>

main()

{

int number;

int valid = 0;

while( valid == 0 ) {

printf(“Enter a number between 1 and 10 à”);

scanf(“%d”, &number);

if( number < 1 ) {

printf(“Number is below 1. Please re-enter\n”);

valid = 0;

}

else if( number > 10 ) {

printf(“Number is above 10. Please re-enter\n”);

valid = 0;

}

else

valid = 1;

}

printf(“The number is %d\n”, number );

}

This program is slightly different from the previous example in that an else clause is used to set the variable valid to 1. In this program, the logic should be easier to follow.

3. NESTED IF ELSE

/* Illustates nested if else and multiple arguments to the scanf function. */

Example:

#include <stdio.h>

main()

{

int invalid_operator = 0;

char operator;

float number1, number2, result;

printf(“Enter two numbers and an operator in the format\n”);

printf(“ number1 operator number2\n”);

scanf(“%f %c %f”, &number1, &operator, &number2);

if(operator == ‘*’)

result = number1 * number2;

else if(operator == ‘/’)

result = number1 / number2;

else if(operator == ‘+’)

result = number1 + number2;

else if(operator == ‘-‘)

result = number1 – number2;

else

invalid_operator = 1;

if( invalid_operator != 1 )

printf(“%f %c %f is %f\n”, number1, operator, number2, result );

else

printf(“Invalid operator.\n”);

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6. Write short notes on the following: (JAN 2009)

‘for’ loop

‘while’ loop

‘dowhile’ loop

‘Switch case ‘ (MAY 2009/FEB 2009/FEB 2010)

BRANCHING AND LOOPING

1. ITERATION, FOR LOOPS

The basic format of the for statement is,

for( start condition; continue condition; re-evaulation )

program statement;

/* sample program using a for statement */

#include <stdio.h>

main() /* Program introduces the for statement, counts to ten */

{

int count;

for( count = 1; count <= 10; count = count + 1 )

printf(“%d “, count );

printf(“\n”);

}

The program declares an integer variable count. The first part of the for statement for (count = 1; initialized the value of count to 1.

The for loop continues with the condition count <= 10; evaluates as TRUE. As

the variable count has just been initialized to 1, this condition is TRUE and so the

program statement printf(“%d “, count ); is executed, which prints the value of count to the screen, followed by a space character.

Next, the remaining statement of the for is executed count = count + 1); which adds one to the current value of count. Control now passes back to the conditional test, count <= 10; which evaluates as true, so the program statement printf(“%d “, count ); is executed.

Count is incremented again, the condition re-evaluated etc, until count reaches a value of

11.

When this occurs, the conditional test count <= 10; evaluates as FALSE, and the for loop terminates, and program control passes to the statement printf(“\n”); which prints a newline, and then the program terminates, as there are no more statements left to execute.

2. THE WHILE STATEMENT

The while provides a mechanism for repeating C statements whilst a condition is

true. Its format is, while( condition ) program statement;

Somewhere within the body of the while loop a statement must alter the value of the condition to allow the loop to finish.

Example:

/* Sample program including while */

#include <stdio.h>

main()

{

int loop = 0;

while( loop <= 10 ) {

printf(“%d\n”, loop);

++loop;

}

}

The above program uses a while loop to repeat the statements

printf(“%d\n”,loop); ++loop; the value of the variable loop is less than or

equal to 10.

3. THE DO WHILE STATEMENT

The do { } while statement allows a loop to continue whilst a condition evaluates as

TRUE (non-zero). The loop is executed as least once.

Example:

/* Demonstration of DO...WHILE */

#include <stdio.h>

main()

{

int value, r_digit;

printf(“Enter the number to be reversed.\n”);

scanf(“%d”, &value);

do {

r_digit = value % 10; printf(“%d”, r_digit); value = value / 10;

} while( value != 0 );

printf(“\n”);

}

The above program reverses a number that is entered by the user. It does this by using the modulus % operator to extract the right most digit into the variable r_digit. The original number is then divided by 10, and the operation repeated whilst the number is not equal to 0.

4. SWITCH CASE:

The switch case statement is a better way of writing a program when a series of if elses occurs.

The general format for this is, switch ( expression ) { case value1:

program statement;

program statement;

...... break;

case valuen:

program statement;

....... break; default:

.......

....... break;

}

The keyword break must be included at the end of each case statement. The default clause is optional, and is executed if the cases are not met. The right brace at the end signifies the end of the case selections.

Example:

#include <stdio.h>

main()

{

int menu, numb1, numb2, total;

printf(“enter in two numbers à”); scanf(“%d %d”, &numb1, &numb2 ); printf(“enter in choice\n”); printf(“1=addition\n”); printf(“2=subtraction\n”);

scanf(“%d”, &menu );

switch( menu ) {

case 1: total = numb1 + numb2; break;

case 2: total = numb1 – numb2; break;

default: printf(“Invalid option selected\n”);

}

if( menu == 1 )

printf(“%d plus %d is %d\n”, numb1, numb2, total );

else if( menu == 2 )

printf(“%d minus %d is %d\n”, numb1, numb2, total );

}

The above program uses a switch statement to validate and select upon the users input choice, simulating a simple menu of choices.

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7. Explain briefly about the input and output function in ‘C’. (MAY 2009/FEB 2009)

1 printf ():

MANAGING INPUT AND OUTPUT OPERATORS

printf() is actually a function (procedure) in C that is used for printing variables and text. Where text appears in double quotes “”, it is printed without modification. There are some exceptions however.

This has to do with the \ and % characters. These characters are modifiers, and

for the present the \ followed by the n character represents a newline character.

Example:

#include <stdio.h>

main()

{

printf(“Programming in C is easy.\n”);

printf(“And so is Pascal.\n”);

}

@ Programming in C is easy. And so is Pascal.

FORMATTERS for printf are, Cursor Control Formatters

\n newline

\t tab

\r carriage return

\f form feed

\v vertical tab

2. Scanf ():

Scanf () is a function in C which allows the programmer to accept input from a

keyboard.

Example:

#include <stdio.h>

main() /* program which introduces keyboard input */

{

int number;

printf(“Type in a number \n”);

scanf(“%d”, &number);

printf(“The number you typed was %d\n”, number);

}

FORMATTERS FOR scanf()

The following characters, after the % character, in a scanf argument, have the

following effect.

D read a decimal integer o read an octal value

x read a hexadecimal value h read a short integer

l read a long integer

f read a float value

e read a double value

c read a single character

s read a sequence of characters

[...] Read a character string. The characters inside the brackets

3. ACCEPTING SINGLE CHARACTERS FROM THE KEYBOARD Getchar, Putchar

getchar() gets a single character from the keyboard, and putchar() writes a single character from the keyboard.

Example:

The following program illustrates this,

#include <stdio.h>

main()

{

int i;

int ch;

for( i = 1; i<= 5; ++i ) { ch = getchar(); putchar(ch);

}

}

The program reads five characters (one for each iteration of the for loop) from the keyboard. Note that getchar() gets a single character from the keyboard, and putchar() writes a single character (in this case, ch) to the console screen.

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8. (a) Describe in detail about type conversions in ‘C’ with example.

(b) Define delimiters. List them. Give an example program using various delimiters.

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9. Explain the following:

· Keywords

· Identifiers

· C character set

· Constant and Volatile variables.

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10. Explain the following:

· break statement with example program

· continue statement with example program

· goto statement with example program