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 Makes names of functions, variables, and macros visible Read a single character Read and returns a single character from the text stream “ standard in ” (stdin) int getchar (); Write a single character Writes a single character c to “ standard out ” (stdout) int putchar (int c);

4. Sample Code #include int main () { int c; c = getchar (); putchar (c); return 0; }

5. Read Ten Chars #include int main () { int c; int i; for (i=0; i<10; i++) { c = getchar(); putchar (c); } return 0; }

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

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

8. Character Counting /* count characters in input */ #include int main () { long nc = 0; while (getchar() != EOF) nc++; printf("%ld\n", nc); return 0; } EOF: Platform dependent: Ctrl-D on Linux Ctrl-Z on Windows

9. Line Counting /* count lines in input */ #include int main() { long numLines = 0; int 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 ==, != Control structures Nested controls Next, we consider how to count the number of ocurrences of characters ‘ 0 ’ to ‘ 9 ’

11. A First (Stupid) Try #include int main() { long num0, num1, …, num9; num0 = num1 = … = num9 = 0; int c; while ((c=getchar()) != EOF) { if (c == ‘0’) num0++; else if (c == ‘1’) num1++; …; } printf (…); return 0; }

12. Arrays #include int main() { long num[10]; int c, 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. Essence of Array An array variable a is just the address of the 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 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 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 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 ? ? ? ? a num

17. An Example #include 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 ? ? ? ? a num

18. An Example #include 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