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

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

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);

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

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

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;

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

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;

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;

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’

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;

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;

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

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 ? ? ?

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 ? ? ?

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 ? ? ?

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 ? ? ?

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 ? ? ?