The document discusses various input/output functions in C including character I/O functions like getchar() and putchar(), string I/O functions like gets() and puts(), and general I/O functions like printf() and scanf(). It provides examples of using these functions to read keyboard input, write output to the screen, read from and write to files. The document also covers format specifiers that can be used with scanf() to read different data types from the input and control skipping or suppressing assignment of certain values.

1. Data I/O
Lecture 14
February 7, 2008

2. Data Input and Output
• Character I/O
– getchar(); putchar();
• String I/O
– gets(); puts();
• General I/O
– printf(); scanf();

3. getchar()
#include <stdio.h>
main()
{
char c;
while ((c = getchar()) != EOF)
printf("n%cn",c);
}
//Accepts character from keyboard and prints it
//Till it sees Ctrl-D which stands for End-Of-File
// EOF is defined in stdio.h

4. putchar()
#include <stdio.h>
main()
{
char c;
while ((c = getchar()) != EOF)
putchar(c);
}
//Prints the character on the screen

5. Inputs/Outputs-previous code
Aa //Inp
Aa //Out
B //Inp
B //Out
Aaa //Inp
Aaa /Out

6. scanf()
%c - single character
%d - decimal integer
%e - Floating point
%f - Floating point
%g - Floating point
%h - Short integer
%i - decimal, hexadecimal or octal integer
%o - octal integer

7. scanf()
%s - String followed by whitespace - null
automatically added
%u - unsigned decimal
%X - hexadecimal
[***] - String with whitespace characters

8. scanf()
#include <stdio.h>
main() {
char item[20];
int partno;
float cost;
scanf(“%s %d %f”,item,&partno,&cost);
printf(“%s %d %f”,item,partno,cost);
}

9. Output
 Kama 2 4.5 //Input
 Kama 2 4.5000 //Output
 Since “n” is a whitespace character
 We may enter each input in different lines or two in
one line and the remaining in the other line.
 What went wrong?
 Nothing went wrong in the above toy code
 Let us see the code in next slide

10. The new code
#include <stdio.h>
main() {
char item[20], item1[20];
int partno, partno1;
float cost, cost1;
scanf(“%s %d %f”,item,&partno,&cost);
scanf(“%s %d %f”,item1,&partno1,&cost1);
printf(“%s %d %fn”,item,partno,cost);
printf(“%s %d %fn”,item1,partno1,cost1);
}

11. Output
Kama 2 4.5 //Input
Vasanth 3 5.6 //Input
Kama 2 4.50000 //Output
Vasanth 3 5.6 //Output

12. Output
Kama 2 4.5re //Input
Vasanth 3 5.6 //Input
Kama 2 4.50000 //Output
re <garbage> <garbage> //Output
 Now, assume that these two scanf functions
are very far off in the code and no I/O
function in between, such problems can
happen.

13. What was the problem
• Input a string with blank space - say
TAMIL NADU
• We saw yesterday - two ways
–
scanf(“%[ ABCDEFGHIJKLMNOPQRSTUVWXYZ]”,line);
– scanf(“%[^n]”,line);

14. The attractive scanf()
#include <stdio.h>
main()
{
int a, b,c;
scanf(“%3d %3d %3d”,&a,&b,&c);
}

15. I/O
If you enter
 1 2 3 then a=1;b=2;c=3;
 123 456 789 then a=123;b=456;c=789;
 123456789 then a=123;b=456;c=789;
 1234 5678 9 then a=123;b=4;c=567;
When reading from a file where the
data is already stored in a given format,
no other go.

16. Reading from file
#include <stdio.h>
main() {
FILE *fpt; /* File/Stream Pointer - points to
next character to be read in a file */
fpt = fopen(“sample.dat”, “r”); //Open for read
if (fpt == NULL)
printf(“n Errorn”);
else { .. }
fclose(fpt); //File has to be closed
}

17. Read Character by Character
#include <stdio.h>
main() {
FILE *fp; char ch, fname[50];
printf(“Enter the Input File name with extensionn”);
gets(fname);
if ((fp = fopen(fname,”r”)) == NULL)
printf(“n File I/O errorn”); else {
fscanf(fp, “%c”,&ch);
while (!feof(fp)) {
printf(“%c”,ch);
fscanf(fp, “%c”,&ch);
}
}
fclose(fp);
}

18. The attractive scanf()
#include <stdio.h>
main()
{
int I; float x; char c;
scanf(“%3d %5f %c”,&i,&x,&c);
}
If you enter 10 256.875 T; answer is i = 10;
x = 256.8 and c = ‘7’

19. The scanf() prefixes
#include<stdio.h>
main() {
short ix,iy;
long lx,ly;
double dx,dy;
scanf(“%hd %ld %lf”,&ix,&lx,&dx);
//short int, long int, double precision
scanf(“%3ho %7lx %12le”,&iy,&ly,&dy);
}
// Short octal 3 characters, long hex and double precision.

20. The scanf() prefixes
#include<stdio.h>
main() {
short ix,iy;
long lx,ly;
double dx,dy;
scanf(“%hd %D %lf”,&ix,&lx,&dx);
//short int, long int, double precision
scanf(“%3ho %7X %12le”,&iy,&ly,&dy);
}
// Upper case for long, i.e. %ld = %D; %lx = X

21. Assignment Suppression
#include <stdio.h>
main() {
char item[20];
int partno;
float cost;
scanf(“ %s %*d %f”, item, &partno, &cost);
}
// partno will not be updated with the new
values. Again useful in FILE I/O

22. No white space in format
#include <stdio.h>
main() {
char c1, c2, c3;
scanf(“ %c%c%c”,&c1,&c2,&c3);
}
Input is a b c, then c1 = a; c2 = blank; c3 = b;
Solution is leave blank in format string or enter
without blanks or use
scanf(“ %c%1s%1s”, &c1,&c2,&c3);

23. Rule
Non-format characters in the character string
are expected to be matched by the same
character in the input data.
#include <stdio.h>
main() {
int j; float x;
scanf(“%d p %f”, &j, &x);
} // If input is 2 p 4.0, then j = 2 and x = 4.0

24. A small detour
• Generating random numbers in C
• The following functions in <stdlib.h>
– srand(u); - Initialize
– rand(); - returns an int
• No initialization then cannot re-create
• Search for solution in huge search space
– Equal probability of getting the required solution.

25. Example
#include <stdio.h>
#include <stdlib.h>
main() {
unsigned i;
int j;
i = 567798;
srand(i); //Random seed
for (j = 1; j <10; j++)
printf("%d n", rand());
}
Output is:
953046398
1917771860
409593197
1347773344
369084052
1262889428
1801733095
61221318
302024713
Output: Same on
every run

26. Change the Seed
#include <stdio.h>
#include <stdlib.h>
main() {
unsigned i;
int j;
i = 14592;
srand(i); //Random seed
for (j = 1; j <10; j++)
printf("%d n", rand());
}
Output is:
245247744
857714815
1702657041
1337291812
299634782
112628859
1020140206
2134488241
629543352

27. No Seed
#include <stdio.h>
#include <stdlib.h>
main() {
int j;
for (j = 1; j <10; j++)
printf("%d n", rand());
}
Output is:
16807
282475249
1622650073
984943658
1144108930
470211272
101027544
1457850878
1458777923
// Default sequence
//Cannot change
//Compiler decides

28. Creative Question
• Given a Black box that takes as input a
lower triangular matrix and an upper
triangular matrix and outputs the
product of the same, use the black box
to multiple two arbitrary square
matrices.