C program.
Example 4.1
The program in Fig.4.1 shows the use of getchar function in an interactive environment.
The program displays a question of YES/NO type to the user and reads the user's response in a single character (Y or N). If the response is Y, it outputs the message
My name is BUSY BEE
otherwise, outputs.
You are good for nothing
Note there is one line space between the input text and output message.
READING A CHARACTER FROM KEYBOARD
Program
#include
main()
{
char answer;
printf("Would you like to know my name?\n");
printf("Type Y for YES and N for NO: ");
answer = getchar(); /* .... Reading a character...*/
if(answer == 'Y' || answer == 'y')
printf("\n\nMy name is BUSY BEE\n");
else
printf("\n\nYou are good for nothing\n");
}
Output
Would you like to know my name?
Type Y for YES and N for NO: Y
My name is BUSY BEE
Would you like to know my name?
Type Y for YES and N for NO: n
You are good for nothing
Fig.4.1 Use of getchar function
Example 4.2
The program of Fig.4.2 requests the user to enter a character and displays a message on the screen telling the user whether the character is an alphabet or digit, or any other special character.
This program receives a character from the keyboard and tests whether it is a letter or digit and prints out a message accordingly. These tests are done with the help of the following functions:
isalpha(character)
isdigit(character)
For example, isalpha assumes a value non-zero (TRUE) if the argument character contains an alphabet; otherwise it assumes 0 (FALSE). Similar is the case with the function isdigit.
TESTING CHARACTER TYPE
Program:
#include
#include
main()
{
char character;
printf("Press any key\n");
character = getchar();
if (isalpha(character) > 0)
printf("The character is a letter.");
else
if (isdigit (character) > 0)
printf("The character is a digit.");
else
printf("The character is not alphanumeric.");
}
Output
Press any key
h
The character is a letter.
Press any key
5
The character is a digit.
Press any key
*
The character is not alphanumeric.
________________________________________________________________________
Fig.4.2 Program to test the character type
Example 4.3
A program that reads a character from keyboard and then prints it in reverse case is given in Fig.4.3. That is, if the input is upper case, the output will be lower case and vice versa.
The program uses three new functions: islower, toupper, and tolower. The function islower is a conditional function and takes the value TRUE if the argument is a lower case alphabet; otherwise takes the value FALSE. The function toupper converts the lower case argument into an upper case alphabet while the function tolower does the reverse.
WRITING A CHARACTER TO THE SCREEN
Program
#include
#include
main()
{
char alphabet;
printf("Enter an alphabet");
putchar('\n'); /* move to next line */
alphabet = getchar();
if (islower(alphabet))
putchar(toupper(alphabet));
else
putchar(tolower(alphabet));
}
Output
Enter an alphabet
a
A
Enter an alphabet
Q
q
Enter an alphabet
z
Z
Fig.4.3 Reading and writing of alphabets in reverse case
Example 4.4
Various input formatting options for reading integers are experimented in the program shown in Fig. 4.4.
The first scanf requests input data for three integer values a, b, and c, and accordingly three values 1, 2, and 3 are keyed in. Because of the specification %*d the value 2 has been skipped and 3 is assigned to the variable b. Notice that since no data is available for c, it contains garbage.
The second scanf specifies the format %2d and %4d for the variables x and y respectively. Whenever we specify field width for reading integer numbers, the input numbers should not contain more digits that the specified size. Otherwise, the extra digits on the right-hand side will be truncated and assigned to the next variable in the list. Thus, the second scanf has truncated the four digit number 6789 and assigned 67 to x and 89 to y. The value 4321 has been assigned to the first variable in the immediately following scanf statement.
READING INTEGER NUMBERS
Program:
main()
{
int a,b,c,x,y,z;
int p,q,r;
printf("Enter three integer numbers\n");
scanf("%d %*d %d",&a,&b,&c);
printf("%d %d %d \n\n",a,b,c);
printf("Enter two 4-digit numbers\n");
scanf("%2d %4d",&x,&y);
printf("%d %d\n\n", x,y);
printf("Enter two integers\n");
scanf("%d %d", &a,&x);
printf("%d %d \n\n",a,x);
printf("Enter a nine digit number\n");
scanf("%3d %4d %3d",&p,&q,&r);
printf("%d %d %d \n\n",p,q,r);
printf("Enter two three digit numbers\n");
scanf("%d %d",&x,&y);
printf("%d %d",x,y);
}
Output
Enter three integer numbers
1 2 3
1 3 -3577
Enter two 4-digit numbers
6789 4321
67 89
Enter two integers
44 66
4321 44
Enter a nine-digit number
123456789
66 1234 567
Enter two three-digit numbers
123 456
89 123
Fig.4.4 Reading integers using scanf
Example 4.5
Reading of real numbers (in both decimal point and exponential notation) is illustrated in Fig.4.5.
READING OF REAL NUMBERS
Program:
main()
{
float x,y;
double p,q;
printf("Values of x and y:");
scanf("%f %e", &x, &y);
printf("\n");
printf("x = %f\ny = %f\n\n", x, y);
printf("Values of p and q:");
scanf("%lf %lf", &p, &q);
printf("\np = %lf\nq = %e",p,q);
printf("\n\np = %.12lf\np = %.12e", p,q);
}
Output
Values of x and y:12.3456 17.5e-2
x = 12.345600
y = 0.175000
Values of p and q:4.142857142857 18.5678901234567890
p = 4.142857142857
q = 1.856789012346e+001
Fig.4.5 Reading of real numbers
Example 4.6
Reading of strings using %wc and %ws is illustrated in Fig.4.6.
The program in Fig.4.6 illustrates the use of various field specifications for reading strings. When we use %wc for reading a string, the system will wait until the wth character is keyed in.
Note that the specification %s terminates reading at the encounter of a blank space. Therefore, name2 has read only the first part of "New York" and the second part is automatically assigned to name3. However, during the second run, the string "New-York" is correctly assigned to name2.
READING STRINGS
Program
main()
{
int no;
char name1[15], name2[15], name3[15];
printf("Enter serial number and name one\n");
scanf("%d %15c", &no, name1);
printf("%d %15s\n\n", no, name1);
printf("Enter serial number and name two\n");
scanf("%d %s", &no, name2);
printf("%d %15s\n\n", no, name2);
printf("Enter serial number and name three\n");
scanf("%d %15s", &no, name3);
printf("%d %15s\n\n", no, name3);
}
Output
Enter serial number and name one
1 123456789012345
1 123456789012345r
Enter serial number and name two
2 New York
2 New
Enter serial number and name three
2 York
Enter serial number and name one
1 123456789012
1 123456789012 r
Enter serial number and name two
2 New-York
2 New-York
Enter serial number and name three
3 London
3 London
Fig. 4.6 Reading of strings
Example 4.7
The program in Fig. 4.7 illustrates the function of %[ ] specification.
ILLUSTRATION OF %[ ] SPECIFICATION
Program-A
main()
{
char address[80];
printf("Enter address\n");
scanf("%[a-z’]", address);
printf("%-80s\n\n", address);
}
Output
Enter address
new delhi 110002
new delhi
ILLUSTRATION OF %[^ ] SPECIFICATION
Program-B
main()
{
char address[80];
printf("Enter address\n");
scanf("%[^\n]", address);
printf("%-80s", address);
}
Output
Enter address
New Delhi 110 002
New Delhi 110 002
Fig.4.7 Illustration of conversion specification%[] for strings
Example 4.8
The program presented in Fig.4.8 illustrates the testing for correctness of reading of data by scanf function.
The function scanf is expected to read three items of data and therefore, when the values for all the three variables are read correctly, the program prints out their values. During the third run, the second item does not match with the type of variable and therefore the reading is terminated and the error message is printed. Same is the case with the fourth run.
In the last run, although data items do not match the variables, no error message has been printed. When we attempt to read a real number for an int variable, the integer part is assigned to the variable, and the truncated decimal part is assigned to the next variable.
Note that the character `2' is assigned to the character variable c.
TESTING FOR CORRECTNESS OF INPUT DATA
Program
main()
{
int a;
float b;
char c;
printf("Enter values of a, b and c\n");
if (scanf("%d %f %c", &a, &b, &c) == 3)
printf("a = %d b = %f c = %c\n" , a, b, c);
else
printf("Error in input.\n");
}
Output Enter values of a, b and c
12 3.45 A
a = 12 b = 3.450000 c = A
Enter values of a, b and c
23 78 9
a = 23 b = 78.000000 c = 9
Enter values of a, b and c
8 A 5.25
Error in input.
Enter values of a, b and c
Y 12 67
Error in input.
Enter values of a, b and c
15.75 23 X
a = 15 b = 0.750000 c = 2
Fig.4.8 Detection of errors in scanf input
Example 4.9
The program in Fig.4.9 illustrates the output of integer numbers under various formats.
PRINTING OF INTEGER NUMBERS
Program:
main()
{
int m = 12345;
long n = 987654;
printf("%d\n",m);
printf("%10d\n",m);
printf("%010d\n",m);
printf("%-10d\n",m);
printf("%10ld\n",n);
printf("%10ld\n",-n);
}
Output
12345
12345
0000012345
12345
987654
-987654
Fig.4.9 Formatted output of integers
Example 4.10
All the options of printing a real number are illustrated in Fig.4.10.
PRINTING OF REAL NUMBERS
Program:
main()
{
float y = 98.7654;
printf("%7.4f\n", y);
printf("%f\n", y);
printf("%7.2f\n", y);
printf("%-7.2f\n", y);
printf("%07.2f\n", y);
printf("%*.*f", 7, 2, y);
printf("\n");
printf("%10.2e\n", y);
printf("%12.4e\n", -y);
printf("%-10.2e\n", y);
printf("%e\n", y);
}
Output 98.7654
98.765404
98.77
98.77
0098.77
98.77
9.88e+001
-9.8765e+001
9.88e+001
9.876540e+001
Fig.4.10 Formatted output of real numbers
Example 4.11
Printing of characters and strings is illustrated in Fig.4.11.
PRINTING OF CHARACTERS AND STRINGS
Program
main()
{
char x = 'A';
static char name[20] = "ANIL KUMAR GUPTA";
printf("OUTPUT OF CHARACTERS\n\n");
printf("%c\n%3c\n%5c\n", x,x,x);
printf("%3c\n%c\n", x,x);
printf("\n");
printf("OUTPUT OF STRINGS\n\n");
printf("%s\n", name);
printf("%20s\n", name);
printf("%20.10s\n", name);
printf("%.5s\n", name);
printf("%-20.10s\n", name);
printf("%5s\n", name);
}
Output
OUTPUT OF CHARACTERS
A
A
A
A
A
OUTPUT OF STRINGS
ANIL KUMAR GUPTA
ANIL KUMAR GUPTA
ANIL KUMAR
ANIL
ANIL KUMAR
ANIL KUMAR GUPTA
Fig.4.11 Printing of characters and strings
