infix do prefiksu za pomocą programu listy CPP Linked
#include <stdio.h>#include <conio.h>#include <string.h>#include <ctype.h>#define MAX 50struct infix{ char target[MAX] ; char stack[MAX] ; char *s, *t ; int top, l ;} ; void initinfix ( struct infix * ) ;void setexpr ( struct infix *, char * ) ;void push ( struct infix *, char ) ;char pop ( struct infix * ) ;void convert ( struct infix * ) ;int priority ( char c ) ;void show ( struct infix ) ; void main( ){ struct infix q ; char expr[MAX] ; clrscr( ) ; initinfix ( &q ) ; printf ( "\nEnter an expression in infix form: " ) ; gets ( expr ) ; setexpr ( &q, expr ) ; convert ( &q ) ; printf ( "The Prefix expression is: " ) ; show ( q ) ; getch( ) ;}/* initializes elements of structure variable */void initinfix ( struct infix *pq ){ pq -> top = -1 ; strcpy ( pq -> target, "" ) ; strcpy ( pq -> stack, "" ) ; pq -> l = 0 ;}/* reverses the given expression */void setexpr ( struct infix *pq, char *str ){ pq -> s = str ; strrev ( pq -> s ) ; pq -> l = strlen ( pq -> s ) ; *( pq -> target + pq -> l ) = '\0' ; pq -> t = pq -> target + ( pq -> l - 1 ) ;}/* adds operator to the stack */void push ( struct infix *pq, char c ){ if ( pq -> top == MAX - 1 ) printf ( "\nStack is full.\n" ) ; else { pq -> top++ ; pq -> stack[pq -> top] = c ; }}/* pops an operator from the stack */char pop ( struct infix *pq ){ if ( pq -> top == -1 ) { printf ( "Stack is empty\n" ) ; return -1 ; } else { char item = pq -> stack[pq -> top] ; pq -> top-- ; return item ; }}/* converts the infix expr. to prefix form */void convert ( struct infix *pq ){ char opr ; while ( *( pq -> s ) ) { if ( *( pq -> s ) == ' ' || *( pq -> s ) == '\t' ) { pq -> s++ ; continue ; } if ( isdigit ( *( pq -> s ) ) || isalpha ( *( pq -> s ) ) ) { while ( isdigit ( *( pq -> s ) ) || isalpha ( *( pq -> s ) ) ) { *( pq -> t ) = *( pq -> s ) ; pq -> s++ ; pq -> t-- ; } } if ( *( pq -> s ) == ')' ) { push ( pq, *( pq -> s ) ) ; pq -> s++ ; } if ( *( pq -> s ) == '*' || *( pq -> s ) == '+' || *( pq -> s ) == '/' || *( pq -> s ) == '%' || *( pq -> s ) == '-' || *( pq -> s ) == '$' ) { if ( pq -> top != -1 ) { opr = pop ( pq ) ; while ( priority ( opr ) > priority ( *( pq -> s ) ) ) { *( pq -> t ) = opr ; pq -> t-- ; opr = pop ( pq ) ; } push ( pq, opr ) ; push ( pq, *( pq -> s ) ) ; } else push ( pq, *( pq -> s ) ) ; pq -> s++ ; } if ( *( pq -> s ) == '(' ) { opr = pop ( pq ) ; while ( opr != ')' ) { *( pq -> t ) = opr ; pq -> t-- ; opr = pop ( pq ) ; } pq -> s++ ; } } while ( pq -> top != -1 ) { opr = pop ( pq ) ; *( pq -> t ) = opr ; pq -> t-- ; } pq -> t++ ;}/* returns the priotity of the operator */int priority ( char c ){ if ( c == '$' ) return 3 ; if ( c == '*' || c == '/' || c == '%' ) return 2 ; else { if ( c == '+' || c == '-' ) return 1 ; else return 0 ; }}/* displays the prefix form of given expr. */void show ( struct infix pq ){ while ( *( pq.t ) ) { printf ( " %c", *( pq.t ) ) ; pq.t++ ; }}
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