Create prefix_evaluation.c

prefix_evaluation.c

@@ -0,0 +1,80 @@
+#include<stdio.h>
+#include<string.h>
+#define MAX 50    
+
+struct Stack
+{          
+int stack[MAX];                                                                                 //A Global Stack
+char prefix[MAX];                                                                               //A Global Prefix Stack
+}eval;     
+
+int top=-1;
+void pushstack(int tmp);                                                                        //push function
+void evaluate(char c);                                                                          //Evaluiate Function
+
+
+int main()
+{ 
+
+    int i,length;
+    printf("Insert a prefix notation ::\n");
+    scanf("%s",eval.prefix);
+    length=strlen(eval.prefix);                                                                  //Length Of the Whole Prefix Expression To Evaluate
+    for(i=length-1;i>=0;i--)
+    {
+        if(eval.prefix[i]>='0' && eval.prefix[i]<='9')
+        {
+          pushstack(i);                                                                           //if the element is a number push it
+        }
+        if(eval.prefix[i]=='+' || eval.prefix[i]=='-' || eval.prefix[i]=='*' || eval.prefix[i]=='/' || eval.prefix[i]=='^')       //if element is an operator
+        {
+          evaluate(eval.prefix[i]);                                                                                               //pass it to the evaluate
+        }
+    }                                                                                        
+   printf("\n\nResult :: %d\n",eval.stack[top]);                                                                                  //print the result from the top
+}
+
+void pushstack(int tmp)                                                                                                           //definiton for push
+{
+   top++;                                                                                                                         //incrementing top
+   eval.stack[top]=(int)(eval.prefix[tmp]-48);                                                                                    //type casting the string to its integer value
+}
+
+void evaluate(char c)                                                                          
+{
+   int storetop,newtop,ans;          
+   storetop=eval.stack[top];                                                                                                       //storetop takes the value stored in the top
+   eval.stack[top]='\0';                                                                                                           //make the stack top NULL as its a string
+   top--;                                                                                                                          
+   newtop=eval.stack[top];                                                                                                         //put the value at new top to newtop
+   eval.stack[top]='\0';                                                                                                           //make it NULL
+   top--;                                                                                     
+   switch(c)                                                                                                                       //check operator been passed to evaluate
+   {
+      case '+':                                                                                
+          ans=storetop+newtop;
+          break;
+      case '-':                                                                               
+          ans=storetop-newtop;
+          break;
+      case '*':                                                                                
+          ans=storetop*newtop;
+          break;
+      case '/':                                                                               
+          ans=storetop/newtop;
+          break;
+      case '^':                                                                               
+          ans=storetop^newtop;
+          break;
+      default:  
+          ans=0;                                                                              
+   }    
+   top++;                                                                                  
+   eval.stack[top]=ans;                                                                                                              //store the answer at top
+}
+
+
+
+
+
+