Create infix_to_prefix.cpp

Program's_Contributed_By_Contributors/CPP/LinkedList/infix_to_prefix.cpp

@@ -0,0 +1,184 @@
+/*  C Program to convert infix to prefix and evaluate prefix expression  */
+
+#include<stdio.h>
+#include<string.h>
+#include<math.h>
+#include<stdlib.h>
+
+#define BLANK ' '
+#define TAB '\t'
+#define MAX 50
+
+long int pop();
+long int eval_pre();
+char infix[MAX], prefix[MAX];
+long int stack[MAX];
+int top;
+int isempty();
+int white_space(char symbol);
+
+void infix_to_prefix();
+int priority(char symbol);
+void push(long int symbol);
+long int pop();
+long int eval_pre();
+
+int main()
+{
+        long int value;
+        top = -1;
+        printf("Enter infix : ");
+        gets(infix);
+        infix_to_prefix();
+        printf("prefix : %s\n",prefix);
+        value=eval_pre();
+        printf("Value of expression : %ld\n",value);
+
+        return 0;
+
+}
+
+void infix_to_prefix()
+{
+        int i,j,p,n;
+        char next ;
+        char symbol;
+        char temp;
+        n=strlen(infix);
+        p=0;
+
+        for(i=n-1; i>=0; i--)
+        {
+                symbol=infix[i];
+                if(!white_space(symbol))
+                {
+                        switch(symbol)
+                        {
+                        case ')':
+                                push(symbol);
+                                break;
+                        case '(':
+                                while( (next=pop()) != ')')
+                                        prefix[p++] = next;
+                                break;
+                        case '+':
+                        case '-':
+                        case '*':
+                        case '/':
+                        case '%':
+                        case '^':
+                                while( !isempty( ) &&  priority(stack[top])> priority(symbol) )
+                                        prefix[p++] = pop();
+                                push(symbol);
+                                break;
+                        default: /*if an operand comes*/
+                             prefix[p++] = symbol;
+                        }
+                }
+        }
+        while(!isempty( ))
+                prefix[p++] = pop();
+        prefix[p] = '\0'; /*End prefix with'\0' to make it a string*/
+
+        for(i=0,j=p-1;i<j;i++,j--)
+        {
+                temp=prefix[i];
+                prefix[i]=prefix[j];
+                prefix[j]=temp;
+        }
+}
+
+/* This function returns the priority of the operator */
+int priority(char symbol )
+{
+        switch(symbol)
+        {
+        case ')':
+                return 0;
+        case '+':
+        case '-':
+                return 1;
+        case '*':
+        case '/':
+        case '%':
+                return 2;
+        case '^':
+                return 3;
+        default :
+                 return 0;
+        }
+}
+void push(long int symbol)
+{
+        if(top > MAX)
+        {
+                printf("Stack overflow\n");
+                exit(1);
+        }
+        else
+        {
+                top=top+1;
+                stack[top] = symbol;
+        }
+}
+
+long int pop()
+{
+        if(top == -1 )
+        {
+                printf("Stack underflow \n");
+                exit(2);
+        }
+        return (stack[top--]);
+}
+
+int isempty()
+{
+        if(top==-1)
+                return 1;
+        else
+                return 0;
+}
+
+int white_space(char symbol)
+{
+        if(symbol==BLANK || symbol==TAB || symbol=='\0')
+                return 1;
+        else
+                return 0;
+}
+
+long int eval_pre()
+{
+        long int a,b,temp,result;
+        int i;
+
+        for(i=strlen(prefix)-1;i>=0;i--)
+        {
+                if(prefix[i]<='9' && prefix[i]>='0')
+                        push( prefix[i]-48 );
+                else
+                {
+                        b=pop();
+                        a=pop();
+                        switch(prefix[i])
+                        {
+                        case '+':
+                                temp=b+a; break;
+                        case '-':
+                                temp=b-a;break;
+                        case '*':
+                                temp=b*a;break;
+                        case '/':
+                                temp=b/a;break;
+                        case '%':
+                                temp=b%a;break;
+                        case '^':
+                                temp=pow(b,a);
+                        }
+                        push(temp);
+                }
+        }
+        result=pop();
+        return result;
+}