diff --git a/DSA_Project1/calc.h b/DSA_Project1/calc.h
index abd4f33..01f3ba2 100644
--- a/DSA_Project1/calc.h
+++ b/DSA_Project1/calc.h
@@ -3,11 +3,6 @@
 
 #define EXPR_MAX 100
 
-typedef struct {
-    double data[EXPR_MAX];
-    int top;
-} numstack;
-
 typedef struct {
     char data[EXPR_MAX];
     int top;
@@ -24,9 +19,6 @@ typedef struct {
     int top;
 } nodestack;
 
-void pushNum(numstack *s, double val);
-double popNum(numstack *s);
-
 void pushOp(opstack *s, char op);
 char popOp(opstack *s);
 char peekOp(opstack *s);
@@ -38,7 +30,14 @@ int precedence(char op);
 double applyOp(double a, double b, char op);
 int isOperator(char c);
 
-double eval(const char *expr);
+Node* createNode(const char *data);
+void infixToPostfix(const char *infix, char *postfix);
+Node* buildTreeFromPostfix(const char *expr);
+Node* buildTreeFromPrefix(const char *expr);
+double evaluateTree(Node *root);
+void freeTree(Node *root);
+
+double eval_Infix(const char *expr);
 double evalPostfix(const char *expr);
 double evalPrefix(const char *expr);
 
diff --git a/DSA_Project1/calculator b/DSA_Project1/calculator
index 3a331a7..7d1ca7a 100755
Binary files a/DSA_Project1/calculator and b/DSA_Project1/calculator differ
diff --git a/DSA_Project1/eval.c b/DSA_Project1/eval.c
index a2cd8ab..9c7931a 100644
--- a/DSA_Project1/eval.c
+++ b/DSA_Project1/eval.c
@@ -5,6 +5,36 @@
 #include <math.h>
 #include "calc.h"
 
+Node* createNode(const char *data) {
+    Node *newNode = (Node*)malloc(sizeof(Node));
+    strcpy(newNode->data, data);
+    newNode->left = NULL;
+    newNode->right = NULL;
+    return newNode;
+}
+
+void freeTree(Node *root) {
+    if (root == NULL) return;
+    freeTree(root->left);
+    freeTree(root->right);
+    free(root);
+}
+
+double evaluateTree(Node *root) {
+    if (root == NULL) return 0;
+    
+    // operand is leaf node
+    if (root->left == NULL && root->right == NULL) {
+        return atof(root->data);
+    }
+    
+    // recursive evaluation
+    double leftVal = evaluateTree(root->left);
+    double rightVal = evaluateTree(root->right);
+    
+    return applyOp(leftVal, rightVal, root->data[0]);
+}
+
 int precedence(char op) {
     if (op == '+' || op == '-') return 1;
     if (op == '*' || op == '/') return 2;
@@ -25,79 +55,77 @@ int isOperator(char c) {
     return (c == '+' || c == '-' || c == '*' || c == '/');
 }
 
-double eval(const char *expr) {
-    numstack values = {.top = -1};
+void infixToPostfix(const char *infix, char *postfix) {
     opstack ops = {.top = -1};
-    int i = 0, len = strlen(expr);
+    int i = 0, k = 0, len = strlen(infix);
 
     while (i < len) {
-        if (isspace(expr[i])) {
+        if (isspace(infix[i])) {
             i++;
             continue;
         }
 
-        if (expr[i] == '-' && (i == 0 || expr[i - 1] == '(')) {// expr[i] == '-' for case of unary minus
-            char numStr[20];
-            int j = 0;
-            numStr[j++] = '-';
+        if (infix[i] == '-' && (i == 0 || infix[i - 1] == '(')) {// unary minus
+            postfix[k++] = '-';
             i++;
 
-            while (i < len && (isdigit(expr[i]) || expr[i] == '.'))
-                numStr[j++] = expr[i++];
+            while (i < len && (isdigit(infix[i]) || infix[i] == '.'))
+                postfix[k++] = infix[i++];
 
-            numStr[j] = '\0';
-            pushNum(&values, atof(numStr));
+            postfix[k++] = ' ';
             continue;
         }
 
-        if (isdigit(expr[i]) || expr[i] == '.') {
-            char numStr[20];
-            int j = 0;
-
-            while (i < len && (isdigit(expr[i]) || expr[i] == '.'))
-                numStr[j++] = expr[i++];
+        if (isdigit(infix[i]) || infix[i] == '.') {
+            while (i < len && (isdigit(infix[i]) || infix[i] == '.'))
+                postfix[k++] = infix[i++];
 
-            numStr[j] = '\0';
-            pushNum(&values, atof(numStr));
+            postfix[k++] = ' ';
         }
-        else if (expr[i] == '(') {
-            pushOp(&ops, expr[i]);
+        else if (infix[i] == '(') {
+            pushOp(&ops, infix[i]);
             i++;
         }
-        else if (expr[i] == ')') {
+        else if (infix[i] == ')') {
             while (ops.top != -1 && peekOp(&ops) != '(') {
-                double b = popNum(&values);
-                double a = popNum(&values);
-                char op = popOp(&ops);
-                pushNum(&values, applyOp(a, b, op));
+                postfix[k++] = popOp(&ops);
+                postfix[k++] = ' ';
             }
             popOp(&ops);
             i++;
         }
-        else {
-            while (ops.top != -1 && precedence(peekOp(&ops)) >= precedence(expr[i])) {
-                double b = popNum(&values);
-                double a = popNum(&values);
-                char op = popOp(&ops);
-                pushNum(&values, applyOp(a, b, op));
+        else if (isOperator(infix[i])) {
+            while (ops.top != -1 && peekOp(&ops) != '(' && precedence(peekOp(&ops)) >= precedence(infix[i])) {
+                postfix[k++] = popOp(&ops);
+                postfix[k++] = ' ';
             }
-            pushOp(&ops, expr[i]);
+            pushOp(&ops, infix[i]);
+            i++;
+        }
+        else {
             i++;
         }
     }
 
     while (ops.top != -1) {
-        double b = popNum(&values);
-        double a = popNum(&values);
-        char op = popOp(&ops);
-        pushNum(&values, applyOp(a, b, op));
+        postfix[k++] = popOp(&ops);
+        postfix[k++] = ' ';
     }
 
-    return popNum(&values);
+    postfix[k] = '\0';
 }
 
-double evalPostfix(const char *expr) {
-    numstack values = {.top = -1};
+double eval_Infix(const char *expr) {
+    char postfix[EXPR_MAX * 2];
+    infixToPostfix(expr, postfix);
+    Node *tree = buildTreeFromPostfix(postfix);
+    double result = evaluateTree(tree);
+    freeTree(tree);
+    return result;
+}
+
+Node* buildTreeFromPostfix(const char *expr) {
+    nodestack nodes = {.top = -1};
     int i = 0, len = strlen(expr);
 
     while (i < len) {
@@ -118,12 +146,17 @@ double evalPostfix(const char *expr) {
                 numStr[j++] = expr[i++];
 
             numStr[j] = '\0';
-            pushNum(&values, atof(numStr));
+            pushNode(&nodes, createNode(numStr));
         }
         else if (isOperator(expr[i])) {
-            double b = popNum(&values);
-            double a = popNum(&values);
-            pushNum(&values, applyOp(a, b, expr[i]));
+            Node *right = popNode(&nodes);
+            Node *left = popNode(&nodes);
+            
+            char opStr[2] = {expr[i], '\0'};
+            Node *opNode = createNode(opStr);
+            opNode->left = left;
+            opNode->right = right;
+            pushNode(&nodes, opNode);
             i++;
         }
         else {
@@ -131,11 +164,18 @@ double evalPostfix(const char *expr) {
         }
     }
 
-    return popNum(&values);
+    return popNode(&nodes);
 }
 
-double evalPrefix(const char *expr) {
-    numstack values = {.top = -1};
+double evalPostfix(const char *expr) {
+    Node *tree = buildTreeFromPostfix(expr);
+    double result = evaluateTree(tree);
+    freeTree(tree);
+    return result;
+}
+
+Node* buildTreeFromPrefix(const char *expr) {
+    nodestack nodes = {.top = -1};
     int len = strlen(expr);
     int i = len - 1;
 
@@ -166,12 +206,17 @@ double evalPrefix(const char *expr) {
             }
 
             numStr[j] = '\0';
-            pushNum(&values, atof(numStr));
+            pushNode(&nodes, createNode(numStr));
         }
         else if (isOperator(expr[i])) {
-            double a = popNum(&values);
-            double b = popNum(&values);
-            pushNum(&values, applyOp(a, b, expr[i]));
+            Node *left = popNode(&nodes);
+            Node *right = popNode(&nodes);
+            
+            char opStr[2] = {expr[i], '\0'};
+            Node *opNode = createNode(opStr);
+            opNode->left = left;
+            opNode->right = right;
+            pushNode(&nodes, opNode);
             i--;
         }
         else {
@@ -179,5 +224,12 @@ double evalPrefix(const char *expr) {
         }
     }
 
-    return popNum(&values);
+    return popNode(&nodes);
+}
+
+double evalPrefix(const char *expr) {
+    Node *tree = buildTreeFromPrefix(expr);
+    double result = evaluateTree(tree);
+    freeTree(tree);
+    return result;
 }
diff --git a/DSA_Project1/gui.c b/DSA_Project1/gui.c
index 0547606..c49e4e9 100644
--- a/DSA_Project1/gui.c
+++ b/DSA_Project1/gui.c
@@ -54,7 +54,7 @@ static void on_calculate_clicked(GtkWidget *widget, gpointer data) {
             result = evalPrefix(expr);
             break;
         default:
-            result = eval(expr);
+            result = eval_Infix(expr);
             break;
     }
     
@@ -113,7 +113,7 @@ static void on_file_open_clicked(GtkWidget *widget, gpointer data) {
                     result = evalPrefix(expr);
                     break;
                 default:
-                    result = eval(expr);
+                    result = eval_Infix(expr);
                     break;
             }
             
diff --git a/DSA_Project1/main.c b/DSA_Project1/main.c
index 5600541..79116ab 100644
--- a/DSA_Project1/main.c
+++ b/DSA_Project1/main.c
@@ -15,8 +15,8 @@ int main(int argc, char *argv[]) {
     printf("2. GUI (Graphical User Interface)\n");
     printf("Enter choice (1-2): ");
     
-    if (scanf("%d", &mode) != 1) {
-        mode = 1; // Default to CLI
+    if (scanf("%d", &mode) != 1) { // Defaults to CLI
+        mode = 1; 
     }
     getchar();
     
@@ -91,7 +91,7 @@ int run_cli() {
                     result = evalPrefix(expr);
                     break;
                 default:
-                    result = eval(expr);
+                    result = eval_Infix(expr);
                     break;
             }
             printf("%s = %.2f\n", expr, result);
@@ -108,7 +108,7 @@ int run_cli() {
                 result = evalPrefix(expr);
                 break;
             default:
-                result = eval(expr);
+                result = eval_Infix(expr);
                 break;
         }
         printf("Result: %.2f\n", result);
diff --git a/DSA_Project1/stack.c b/DSA_Project1/stack.c
index 1d56fd8..a686cb1 100644
--- a/DSA_Project1/stack.c
+++ b/DSA_Project1/stack.c
@@ -2,14 +2,6 @@
 #include <stdlib.h>
 #include "calc.h"
 
-void pushNum(numstack *s, double val) {
-    s->data[++(s->top)] = val;
-}
-
-double popNum(numstack *s) {
-    return s->data[(s->top)--];
-}
-
 void pushOp(opstack *s, char op) {
     s->data[++(s->top)] = op;
 }
diff --git a/DSA_Project1/test.txt b/DSA_Project1/test.txt
index 75d1bbb..205e24e 100644
--- a/DSA_Project1/test.txt
+++ b/DSA_Project1/test.txt
@@ -1,2 +1,7 @@
 ((11-1) * 5) + 2
-10+1
\ No newline at end of file
+10+1
+15*2+8-4
+(20-5)/(3+2)
+100*2-50+25
+7+8*2-3/3
+(6+4)*(9-3)/2
\ No newline at end of file
diff --git a/DSA_Project1/test_cases.txt b/DSA_Project1/test_cases.txt
new file mode 100644
index 0000000..978aaaf
--- /dev/null
+++ b/DSA_Project1/test_cases.txt
@@ -0,0 +1,11 @@
+=== Infix Expressions ===
+3+5*2 = 13.00
+(10+5)*2-3 = 27.00
+
+=== Postfix Expressions ===
+3 5 2 * + = 13.00
+10 5 + 2 * 3 - = 3
+
+=== Prefix Expressions ===
++ 3 * 5 2 = 13.00
+- * + 10 5 2 3 = 27.00