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  • C lang:character input and output (I/O)

    Xx_Introduction

    • Character input and output is by more line character conpose of the text flow 
    • Define name common use capital  letter,easy read.
    • The Standard C Library ----->provide I/O model ------>use character flow way.

    Ax_Application

    • file copy,charater count,line count,word count

    Bx_Method

    • I/O model common use getchar and putchar,interactive use of putchar and printf. 
      1 getchar()     //read next character
2 putcahr()     //print next character
3 printf()        //print next(bunch) character
    • File Copy
      • file copy version 1 
         1 #include<stdio.h>
 2 
 3 int main()
 4 {
 5     int c;
 6     
 7     c = getchar();
 8     while(c != EOF){
 9         putchar(c);
10         c = getchar();
11     }
12 }
      • file copy version 2 
         1 #include<stdio.h>
 2 
 3 int main()
 4 {
 5     int c;
 6     
 7     while((c = getchar())!= EOF){
 8         putchar(c);
 9     }
10 }

        != : unequal to. priority overtop assignment(=)             EOF:end of file

      • Conclusion:computer use bit storage of character and any data type.
      • Assignment can portion of expression.
      • Complex statement simple easy read,but so hard understand.
      • Due to unequal to relational operator(!=) priority not overtop assignment(=),so c expression use bracket. 
         1 #include <stdio.h>
 2 
 3 int main()
 4 {
 5     int c;
 6 
 7     while (c = getchar() != EOF){
 8         printf("%d
",c);
 9     }
10     printf("%d - at EOF
",c);
11     return 0;
12 }

        if not use bracket,will priority operation EOF,value by 1,if input end or else print "c - at EOF".

      • Print EOF value programming 
        1 #include <stdio.h>
2 
3 int main()
4 {
5     printf("EOF is %d
",EOF);
6     return 0;
7 }

        character constant EOF is in <stdio.h> file definition,value by -1 

      • In other system can by definition other value. 
    • Charater Count(2019-10-8 update)
      • Character count version 1 
         1 #include <stdio.h>
 2 
 3 int main()
 4 {
 5     // version 1
 6     long nc;
 7 
 8     nc = 0;
 9     while (getchar() != EOF)
10         ++nc;
11     printf("%ld
",nc-1);
12     return 0;
13 }

        ++(--) is operater, be euivalent to eg(nc = nc + 1);impression add one.

      • ++(--) use a prefix effect in variable before add.in suffix it's first call variable before use progressive increase.
      • Long than int more big,long support 32bit int support 16bit,but different system imparity,long in printf use %ld.
      • Character version 2 
        1 #include <stdio.h>
2 int main()
3 {
4     double nc;
5     for (nc = 0; getchar() != EOF;++nc)
6     ;
7     printf("%.0f
", nc-1);
8     return 0;
9 }

        double and float use %f format output.double more than float.

      • For circulation a circulation body must exsit,null statement for alone semicolon(;).
      • Important is circulation in execute programs before must judge test condition whether it meets. 
    • Line Count
      • mind:line equal to line break number.
      • Line count program 
         1 #include <stdio.h>
 2 int main()
 3 {
 4     int c,nl;
 5 
 6     nl = 0;
 7     while ((c = getchar()) != EOF)
 8         if (c == '
')
 9             ++nl;
10     printf("%d
",nl);
11     return 0;
12 }

         ==:mean equal.      'A':mean character constant.corresponding ASCII number.

    • Count blanks,tabs,and newlines.

      • version 1

      •  1 #include <stdio.h>
 2 int main()
 3 {
 4     int c, nb, nt, nl;
 5 
 6     nb = 0;     /* number of blanks     */
 7     nt = 0;     /* number of tabs       */
 8     nl = 0;     /* number of newlines   */
 9     while ((c = getchar()) != EOF){
10         if ( c == ' ')
11             ++nb;
12         if ( c == '	')
13             ++nt;
14         if ( c == '
')
15             ++nl;
16     }
17     printf("blanks:%6d
tabs:%6d
newlines:%6d
", nb, nt, nl);
18     return 0;
19 }

        ....>>>

      • version 2 
         1 #include <stdio.h>
 2 int main()
 3 {
 4     int c, nb, nt, nl;
 5 
 6     nb = 0;     /* number of blanks     */
 7     nt = 0;     /* number of tabs       */
 8     nl = 0;     /* number of newlines   */
 9     while ((c = getchar()) != EOF)
10         if ( c == ' ')
11             ++nb;
12         else ( c == '	')
13             ++nt;
14         else ( c == '
')
15             ++nl;
16 
17     printf("blanks:%6d
tabs:%6d
newlines:%6d
", nb, nt, nl);
18     return 0;
19 }
        View Code

        but I not  successful execute.

    • Replace string of blanks with a single blank
      • version 1 
         1 #include <stdio.h>
 2 #define NONBLANK 'a'
 3 int main()
 4 {
 5     int c, lastc;
 6 
 7     lastc = NONBLANK;
 8     while (( c = getchar()) != EOF){
 9         if (c != ' ')
10             putchar(c);
11         if (c == ' ')
12             if (lastc != ' ')
13                 putchar(c);
14         lastc = c;
15     }
16     return 0;
17 }
        View Code

        one if statement control nonblank output.tow if statement deal with blank.three blank check blank is one or more blank.last print c.

      • version 2

         1 #include<stdio.h>
 2 #define NONBLANK 'a'
 3 int main()
 4 {
 5     int c, lastc;
 6 
 7     lastc = NONBLANK;
 8     while ((c = getchar()) != EOF ){
 9         if (c != ' ')
10             putchar(c);
11         else if (lastc != ' ')
12             putchar(c);
13         lastc = c;
14     }
15     return 0;
16 }
        View Code

        ok,success!

      • version 3 
         1 #include <stdio.h>
 2 
 3 #define NONBLANK 'a'
 4 int main()
 5 {
 6     int c, lastc;
 7 
 8     lastc = NONBLANK;
 9     while ((c = getchar()) != EOF){
10         if (c != ' ' || lastc != ' ')
11             putchar(c);
12         lastc = c;
13     }
14     return 0;
15 }
        View Code

        this method use logic simbol (OR) || realize.

      •  ok,this aim at blank deal wilth three method.

    • Replace tabs and backspaces with visible characters.
      • Realize 
         1 #include<stdio.h>
 2 int main()
 3 {
 4     int c;
 5 
 6     while ((c = getchar())!= EOF){
 7         if (c == '	')
 8             printf("\t");
 9         if (c == '')
10             printf("\b");
11         if (c == '\')
12             printf("\\");
13         if (c != '')
14             if (c != '	')
15                 if (c != '\')
16                     putchar(c);
17     }
18     return 0;
19 }
        View Code

         why？//？？？？？？？？？？？？？？？？？？？？？？------------------------------program bug.......I brain in the blue screen.so,go to www.baidu.com to find out.

      • Truth  to version 2 
         1 #include<stdio.h>
 2 int main()
 3 {
 4     int c;
 5 
 6     while ((c = getch())!= EOF){              /*getchar not identify keyboard backspace.*/
 7         if (c == '	')
 8             printf("\t");
 9         if (c == '')
10             printf("\b");
11         if (c == '\')
12             printf("\\");
13         if (c != '')
14             if (c != '	')
15                 if (c != '\')
16                     putchar(c);
17     }
18     return 0;
19 }
        View Code

        getchar not catch backspace so,will getchar replace getch. getch() can catch any print behavior.

      •  oh,yes!

      • It can also be used if-else. to version 3 
         1 #include <stdio.h>
 2 int main()
 3 {
 4     int c;
 5 
 6     while((c = getch())!= EOF)
 7         if (c == '	')
 8             printf("\t");
 9         else if (c == '')
10             printf("\b");
11         else if (c == '\')
12             printf("\\");
13         else
14             putchar(c);
15     return 0;
16 }
        View Code

        ok.next is a word count.

    • word count
      • count input lines,words and strings number. 
         1 #include <stdio.h>
 2 #define IN 1
 3 #define OUT 0
 4 
 5 int main()
 6 {
 7     int c, nl, nw, nc, state;
 8 
 9     state = OUT;
10     nl = nw = nc = 0;
11     while ((c = getchar())!= EOF){
12         ++nc;
13         if (c == '
')
14             ++nl;
15         if (c == ' ' || c == '
' || c == '	')
16             state = OUT;
17         else if (state == OUT){
18             state = IN;
19             ++nw;
20         }
21     }
22     printf("lines:%9d
word:%9d
string:%9d
",nl,nw,nc);
23     return 0;
24 }
        View Code

        &&:AND  ||: OR , AND higher priority OR. expression from left to right.         a = b = c = 0   if meanwhile include value and assignment two type,order from right to left.

      • IF statement 
        1 if(expression)
2     statement1       /* true */
3 else
4     statement2       /* false */
5 else if (expression){
6     statement1       /* true*/
7     ...
8 }

        true or false.

    • Print input one word per line.
      • last practical program.very basis.very important. 
         1 #include<stdio.h>
 2 
 3 #define IN 1
 4 #define OUT 0
 5 
 6 int main()
 7 {
 8     int c, state;
 9 
10     state = OUT;
11     while ((c = getchar()) != EOF){
12         if (c == ' ' || c == '
' || c == '	'){
13             if (state == IN){
14                 putchar('
');
15                 state = OUT;
16             }
17         } else if (state == OUT){
18             state = IN;
19             putchar(c);
20         } else
21             putchar(c);
22     }
23     return 0;
24 }
        View Code

        state is a BOOL value.

    Cx_Conclusion

    1. I/O model common use getchar and putchar,interactive use of putchar and printf.
    2. File Copy
    3. Charater Count
    4. Line Count
    5. Count blanks,tabs,and newlines.
    6. Replace string of blanks with a single blank
    7. Replace tabs and backspaces with visible characters.
    8. word count
    9. Print input one word per line.
    10. getchar and putchar printf().and putch()
    11. != and ===
    12. ++ / -- 
    13. EOF
    14. LONG and DOUBLE
    15. while and if else
    16. ASCII 'A'
    17. || OR  ; && AND
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  • 原文地址：https://www.cnblogs.com/enomothem/p/11632748.html
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