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Prefix to Infix help please

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Prefix to Infix help please

 
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  #1
May 18th, 2006
I'm supposed to take user input in the form of a prefix expression, convert it to infix and postfix, and then print the results. So far, I've got both working, but I would like to add some parenthesis to the infix expression once its converted. At the moment, I can't think of a way to sneak it in there.

Here's my code so far.

C Syntax (Toggle Plain Text) 
  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <string.h>
  4. #include <ctype.h>
  5.  
  6. static char s[50], i;
  7. static char a[50];
  8.  
  9. void push(int data) {
  10. 	s[i++] = data;
  11. }
  12.  
  13. char pop() {
  14. 	return s[--i];
  15. }
  16.  
  17. // prefix -> infix
  18. // prefix -> postfix
  19. void prefix() {
  20.  
  21. 	puts("Enter a prefix expression:");
  22. 	fgets(a, 50, stdin);
  23. 	int a_size = strlen(a);
  24.  
  25. 	puts("Prefix -> Infix:");
  26. 	char *token, delim[] = {" \n"}, match[] = {"*+/-"};
  27. 	int j = 0, m_size = strlen(match);
  28. 	token = strtok(a, delim);
  29. 	while (token != NULL) {
  30. 		if (isdigit(*token)) {
  31. 			printf("%d ", atoi(token));
  32. 			if (i >= 0)	printf("%c ", pop());
  33. 		}
  34. 		else
  35. 			while (j < m_size) {
  36. 				if (*token == match[j]) {
  37. 					push(*token);
  38. 					break;
  39. 				}
  40. 				j++;
  41. 			}		
  42. 		token = strtok(NULL, delim);
  43. 		j = 0;
  44. 	}
  45.  
  46. 	puts("");
  47. 	puts("Prefix -> Postfix:");
  48. 	int k = a_size;
  49. 	while (k >= 0) {
  50. 		if (a[k] == '\0' || a[k] == ' ') k--;
  51. 		printf("%c ", a[k--]);
  52. 	}
  53. 	puts("");
  54. }
  55.  
  56. void infix() {
  57.  
  58. 	puts("Enter an infix expression:");
  59. 	fgets(a, 50, stdin);
  60.  
  61.  
  62. }
  63.  
  64. void postfix() {
  65. }
  66.  
  67. void main(void) {
  68.  
  69. 	int c;
  70. 	puts("1: Prefix");
  71. 	puts("2: Infix");
  72. 	puts("3: Postfix");
  73. 	scanf("%d", &c);
  74. 	fflush(stdin);
  75.  
  76. 	prefix();
  77. 	/*
  78. 	switch(c) {
  79. 		case 1: prefix();
  80. 			break;
  81. 		case 2: infix();
  82. 			break;
  83. 		case 3: postfix();
  84. 			break;
  85. 	}
  86. 	*/
  87. }
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Re: Prefix to Infix help please

 
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  #2
May 18th, 2006
My first bit of advice would be to clean it up a little first.
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PC-lint for C/C++ (NT) Vers. 8.00u, Copyright Gimpel Software 1985-2006

--- Module: test.c (C)
test.c 10 [Info 734] Loss of precision (assignment) (31 bits to 7 bits)
test.c 22 [Warning 534] Ignoring return value of function 'fgets(char *, int, FILE *)'
test.c 23 [Info 713] Loss of precision (initialization) (unsigned int to int)
test.c 27 [Info 713] Loss of precision (initialization) (unsigned int to int)
test.c 51 [Warning 676] Possibly negative subscript (-1) in operator '[' [Reference: file test.c: line 51]
test.c 59 [Warning 534] Ignoring return value of function 'fgets(char *, int, FILE *)'
test.c 6 [Info 728] Symbol 'i' (line 6, file test.c) not explicitly initialized

--- Global Wrap-up
test.c 56 [Info 714] Symbol 'infix(void)' (line 56, file test.c) not referenced
test.c 64 [Info 714] Symbol 'postfix(void)' (line 64, file test.c) not referenced

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
test.c:
Warning W8071 test.c 10: Conversion may lose significant digits in function push
Error E2140 test.c 23: Declaration is not allowed here in function prefix
Error E2140 test.c 26: Declaration is not allowed here in function prefix
Error E2140 test.c 27: Declaration is not allowed here in function prefix
Warning W8065 test.c 32: Call to function 'pop' with no prototype in function prefix
Error E2140 test.c 48: Declaration is not allowed here in function prefix
Warning W8065 test.c 76: Call to function 'prefix' with no prototype in function main
*** 4 errors in Compile ***
The compiler errors are due to compiling as C++, but the others are worth a look. Some of the lint can be overlooked, but it's always worth looking into and finding out the reason behind the diagnostic.

And this always needs fixin':
C Syntax (Toggle Plain Text) 
  1. scanf("%d", &c);
  2. fflush(stdin);
User Input: Strings and Numbers [C]

Add in not using void main, and it might look like something I'd consider looking into. [I'm not trying to be offensive if it may sound so, I just hate rewriting the same stuff over and over and over...]
"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand
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Re: Prefix to Infix help please

 
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  #3
May 18th, 2006
I hate these new quote tags. And what is it with the slider. It doesn't look nice at all. Plz bring back old ones.
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Re: Prefix to Infix help please

 
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  #4
May 19th, 2006
>So far, I've got both working

wouldn't it be better to have an infix to postfix converter?

>I would like to add some parenthesis to the infix expression once its converted. At the moment, I can't think of a way to sneak it in there.

This is not something you can just hope to sneak in. You have to plan it very carefully, from the onset of your program.
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