1. Character Input and Output
C and Data Structures
Baojian Hua

2. Overview We have talked about: This lecture:
Basic data types and C control structures
This lecture:
Basic character input and output
Three examples:
echo input directly to output
character counting
line counting

3. Char IO Including the Standard Input/Output (stdio) library
#include <stdio.h>
Makes names of functions, variables, and macros available
Defining procedure main()
Starting point of the program, a standard boilerplate
Read a single character
Returns a single character from the text stream “standard in” (stdin)
char c = getchar();
Write a single character
Writes a single character to “standard out” (stdout)
putchar (c);

4. The Code #include <stdio.h> int main(void) { int c;
c = getchar();
putchar(c);
return 0; }

5. Read Ten Chars #include <stdio.h> int main(void) { int c; int i;
for (i=0; i<10; i++)
c = getchar();
putchar(c); }
return 0;
self-increment operator

6. Infinite IO #include <stdio.h> // or a while version
int main(void) {
int c;
int i;
for ( ; ; )
c = getchar();
putchar(c); }
return 0;
// or a while version
#include <stdio.h>
int main(void) {
int c;
int i;
while (1)
c = getchar();
putchar(c); }
return 0;

7. Conditional IO #include <stdio.h> int main(void) { int c; int i;
c = getchar();
while (c != ‘a’)
putchar(c); }
return 0;

8. Character Counting #include <stdio.h>
/* count characters in input */
int main() {
long nc;
nc = 0;
while (getchar() != EOF)
++nc; }
printf("%ld\n", nc);
return 0;

9. Line Counting #include <stdio.h> /* count lines in input */
int main() {
long numLines;
numLines = 0; char c;
while ((c=getchar()) != EOF)
if (c == ‘\n’)
++numLines; }
printf("%ld\n", numLines);
return 0;

10. Arrays Thus far, we have seen:
Characters are just small integers (0-255)
More operations
++i, i++, ==, !=
Control structures
Nested controls
Next, we consider how to count the number of characters ‘0’ to ‘9’

11. A First Try #include <stdio.h> int main() {
long num0, num1, …, num9;
num0 = num1 = … = num9 = 0; char c;
while ((c=getchar()) != EOF) {
if (c == ‘0’)
++num0;
else if (c == ‘1’)
++num1; …; }
printf("%ld\n", …);
return 0;

12. Using Arrays #include <stdio.h> int main() { long num[10];
char c;
int i;
for (i=0; i<10; i++)
num[i] = 0;
while ((c=getchar()) != EOF)
if ((c >= ‘0’) && (c <= ‘9’))
++num[c-’0’]; }
return 0;

13. The Essence of Array
An array variable a is just a pointer pointing to the first array element a[0]
So when we pass an array to other functions, or we operate on the array variable, we are really operating on a pointer, not on array elements
More on this later

14. An Example #include <stdio.h> void foo(long[] a) { a[0] = 999;
return; }
int main()
long num[5];
num[0] = 0;
foo (num);
printf(“%ld\n”, num[0]);
return 0; ? ?
num ? ? ?

15. An Example #include <stdio.h> void foo(long[] a) { a[0] = 999;
return; }
int main()
long num[5];
num[0] = 0;
foo (num);
printf(“%ld\n”, num[0]);
return 0; ?
num ? ? ?

16. An Example #include <stdio.h> void foo(long[] a) { a[0] = 999;
return; }
int main()
long num[5];
num[0] = 0;
foo (num);
printf(“%ld\n”, num[0]);
return 0; a ?
num ? ? ?

17. An Example #include <stdio.h> void foo(long[] a) { a[0] = 999;
return; }
int main()
long num[5];
num[0] = 0;
foo (num);
printf(“%ld\n”, num[0]);
return 0; a
999 ?
num ? ? ?

18. An Example #include <stdio.h> void foo(long[] a) { a[0] = 999;
return; }
int main()
long num[5];
num[0] = 0;
foo (num);
printf(“%ld\n”, num[0]);
return 0;
999 ?
num ? ? ?