added postfix evaluation in c

Author: GauravWalia19

C/Data-Structures/STACKS/MISC-STACKS/postfix_evaluation.c

@@ -0,0 +1,82 @@
+#include <stdio.h>
+#define SIZE 100
+#include <math.h>
+#include <stdlib.h>
+/*my own stack*/
+int Stack[SIZE];
+int top = -1;
+int isEmpty()
+{
+  return top == -1;
+}
+
+void push(int item)
+{
+  Stack[++top] = item;
+}
+
+int pop()
+{
+  if(isEmpty())
+  {
+    printf("STACK UNDERFLOW\n");
+    exit(0);
+  }
+  int temp = Stack[top];
+  top--;
+  return temp;
+}
+
+int evalPostfix(char *exp)
+{
+  int i = 0;
+  char str[50];
+  int j = 0;
+  //parsing
+  while (exp[i] != '\0')
+  {
+    if (exp[i] >= '0' && exp[i] <= '9')
+    {
+      push(exp[i] - '0');
+    }
+    else //operator
+    {
+      if(isEmpty())
+      {
+        return -1;
+      }
+      int b = pop();
+      int a = pop();
+      int result = 0;
+      switch (exp[i])
+      {
+      case '+':
+        result = a + b;
+        break;
+      case '-':
+        result = a - b;
+        break;
+      case '/':
+        result = a / b;
+        break;
+      case '*':
+        result = a * b;
+        break;
+      case '^':
+        result = (int)pow(a, b);
+      }
+      push(result);
+    }
+    i++;
+  }
+  return Stack[top];
+}
+
+int main()
+{
+  char str[SIZE];
+  printf("Enter the postfix expression\n");
+  scanf("%s", str);
+  int result = evalPostfix(str);
+  printf("RESULT: %d\n", result);
+}

C/README.md

@@ -36,6 +36,7 @@
 * LINKED STACK
 * MISC
   * [Minimum bracket reversal for balanced expression](Data-Structures/STACKS/MISC-STACKS/minimum_bracket_reversal_for_balanced_expression.c)
+  * [Postfix Evaluation](Data-Structures/STACKS/MISC-STACKS/postfix_evaluation.c)
 
 #### HEAPS
 

datastructures.md

@@ -140,6 +140,13 @@ Indexer for Data Structures Lover
 * implementation
   * [C](C/Data-Structures/STACKS/MISC-STACKS/minimum_bracket_reversal_for_balanced_expression.c)
 
+##### Postfix Evaluation
+
+* blog
+* docs
+* implementation
+  * [C](C/Data-Structures/STACKS/MISC-STACKS/postfix_evaluation.c)
+
 ##### TWO WAY STACK
 
 * blog