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C Homework

C Homework. Write mypaste. c and mycomm.c mypaste is like paste & mycomm is like comm Both take two files as arguments Paste reads a line from each file and outputs them to stdout on the same line

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C Homework

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  1. C Homework • Write mypaste.c and mycomm.c • mypasteis like paste & mycomm is like comm • Both take two files as arguments • Paste reads a line from each file and outputs them to stdout on the same line • Commcompares the two lines with strcmpand outputs the one that comes first in alphabetical order (with the appropriate number of tabs)

  2. hello.c • #include <stdio.h>main(){printf("hello, world\n");} • New Concepts • C is a compiled • Interpreted languages: python, javascript, R, lisp • cc –o hello hello.c • ./hello

  3. Make • make clean • make all • Makefile

  4. Input/Output: mycat.c (My Cat) • #include <stdio.h>main(){int c; while((c = getchar()) != EOF)putchar(c);} • New Concepts • Stdio: getchar/putchar • Variable declarations

  5. mywc.c (My Word Count) • #include <stdio.h>#include <ctype.h>main(){int c, bytes=0, words=0, lines=0;intprev_state=0; while((c = getchar()) != EOF) { bytes++; if(c == '\n') lines++;intcurrent_state = isalnum(c) || ispunct(c); if(!prev_state && current_state) words++;prev_state = current_state; }printf("%d\t%d\t%d\n", lines, words, bytes);} • New Concepts • ++ • ‘\n’ • printf • isalnum, ispunct • man isalnum IN OUT words++ words++

  6. mywc2.c: ac & av • #include <stdio.h>#include <ctype.h>void wc_fd(FILE *fd, char *filename){ int c, bytes=0, words=0, lines=0;intprev_state=0; while((c = getc(fd)) != EOF) { bytes++; if(c == '\n') lines++;intcurrent_state = isalnum(c) || ispunct(c); if(!prev_state && current_state) words++;prev_state = current_state; }printf("%d\t%d\t%d\t%s\n", lines, words, bytes, filename); if(fd && (fd != stdin))fclose(fd);} • void wc(char *filename){ if(strcmp(filename, "-") == 0) {wc_fd(stdin, filename); return; } FILE *fd = fopen(filename, "r"); if(!fd) printf("NA\tNA\tNA\t%s\n", filename); else wc_fd(fd, filename);}int main(int ac, char **av){inti; for(i=0;i<ac;i++)fprintf(stderr, "av[%d] = %s\n", i, av[i]); if(ac <= 1) wc("-"); else for(i = 1; i<ac; i++)wc(av[i]);}

  7. Pointer Addition • #include <stdio.h>main(){ char *str = "hello, world\n"; for( ; *str; str++)printf("%s", str);}

  8. hello3 • #include <stdio.h>#define MAXLINE 1024int main(){ char line[MAXLINE];while(fgets(line, MAXLINE, stdin) != NULL) { char *str = line; for( ; *str; str++)if(str == line || (isblank(str[-1]) && !isblank(str[0])))printf("%s", str); }} • Subscripting • x[i] • (x+i)[0] • *(x+i)

  9. Concepts so far… • Interpreted v. Compiled • cc, gcc, make • stdio • Variable declarations • Strings: pointers to sequences of characters • Pointer addition • Subscripting by positive & negative numbers • x[i] • (x+i)[0] • *(x+i)

  10. Structures • struct box {int ptr:30; unsigned int type:2;};struct pair {struct box first, rest;} heap[HEAPSIZE];

  11. Boxes: Pointer + Type • 3 Types • SYMBOL • nil, +, *, quote • LIST • first + rest • NUMBER • int

  12. first(cons(left, right))  left rest(cons(left, right))  right

  13. Pname: Symbol  StringIntern: String  Symbol

  14. Read, Eval, Print

  15. Eval • Done: addition • To do: subtraction, multiplication, division

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