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Create prefix_evaluation.c

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Solved Issued Of Problem Infix Evaluation
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Jayan 2023-10-02 13:53:25 +05:30 committed by GitHub
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#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
}