Character Input and Output

1. Character Input and Output C and Data Structures Baojian Hua bjhua@ustc.edu.cn

2. Overview • We have talked about: • 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. self-increment operator 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; }

6. Infinite IO #include <stdio.h> 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’) { c = getchar(); 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; } 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 0 ? 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 ? ? ?