diff --git a/DS/C/Lab/Week5/InfixToPostfix.c b/DS/C/Lab/Week5/InfixToPostfix.c
new file mode 100644
index 0000000..b543de6
--- /dev/null
+++ b/DS/C/Lab/Week5/InfixToPostfix.c
@@ -0,0 +1,71 @@
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+#define MAX_SIZE 100
+
+char stack[MAX_SIZE];
+int top = -1;
+
+void push(char item) {
+    if (top >= MAX_SIZE - 1) {
+        printf("Stack Overflow\n");
+        return;
+    }
+    stack[++top] = item;
+}
+
+char pop() {
+    if (top < 0) {
+        printf("Stack Underflow\n");
+        return -1;
+    }
+    return stack[top--];
+}
+
+int precedence(char symbol) {
+    switch (symbol) {
+        case '^': return 3;
+        case '*':
+        case '/': return 2;
+        case '+':
+        case '-': return 1;
+        default: return 0;
+    }
+}
+
+void infixToPostfix(char infix[], char postfix[]) {
+    int i, j = 0;
+    char symbol, next;
+    for (i = 0; i < strlen(infix); i++) {
+        symbol = infix[i];
+        if (isalnum(symbol)) {
+            postfix[j++] = symbol;
+        } else if (symbol == '(') {
+            push(symbol);
+        } else if (symbol == ')') {
+            while ((next = pop()) != '(') {
+                postfix[j++] = next;
+            }
+        } else {
+            while (top > -1 && precedence(stack[top]) >= precedence(symbol)) {
+                postfix[j++] = pop();
+            }
+            push(symbol);
+        }
+    }
+    while (top > -1) {
+        postfix[j++] = pop();
+    }
+    postfix[j] = '\0';
+}
+
+int main() {
+    char infix[MAX_SIZE], postfix[MAX_SIZE];
+    printf("Enter infix expression: ");
+    fgets(infix, MAX_SIZE, stdin);
+    infix[strcspn(infix, "\n")] = 0;  // Remove newline if present
+    infixToPostfix(infix, postfix);
+    printf("Postfix expression: %s\n", postfix);
+    return 0;
+}
\ No newline at end of file
diff --git a/DS/C/Lab/Week5/PostfixCheck.c b/DS/C/Lab/Week5/PostfixCheck.c
new file mode 100644
index 0000000..770015b
--- /dev/null
+++ b/DS/C/Lab/Week5/PostfixCheck.c
@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <string.h>
+
+#define MAX_SIZE 100
+
+int stack[MAX_SIZE];
+int top = -1;
+
+void push(int item) {
+    if (top >= MAX_SIZE - 1) {
+        printf("Stack Overflow\n");
+        return;
+    }
+    stack[++top] = item;
+}
+
+int pop() {
+    if (top < 0) {
+        printf("Stack Underflow\n");
+        return -1;  // Return a sentinel value instead of exiting
+    }
+    return stack[top--];
+}
+
+int isDigit(char c) {
+    return c >= '0' && c <= '9';
+}
+
+int evaluatePostfix(char* exp) {
+    int i, operand1, operand2, result;
+    
+    for (i = 0; exp[i] != '\0'; i++) {
+        if (isDigit(exp[i])) {
+            push(exp[i] - '0');
+        } else {
+            operand2 = pop();
+            operand1 = pop();
+            switch (exp[i]) {
+                case '+': push(operand1 + operand2); break;
+                case '-': push(operand1 - operand2); break;
+                case '*': push(operand1 * operand2); break;
+                case '/': 
+                    if (operand2 == 0) {
+                        printf("Error: Division by zero\n");
+                        return -1;  // Return a sentinel value instead of exiting
+                    }
+                    push(operand1 / operand2); 
+                    break;
+            }
+        }
+    }
+    return pop();
+}
+
+int main() {
+    char exp[MAX_SIZE];
+    printf("Enter a postfix expression: ");
+    fgets(exp, MAX_SIZE, stdin);
+    exp[strcspn(exp, "\n")] = 0;  // Remove newline if present
+    
+    int result = evaluatePostfix(exp);
+    if (result != -1) {
+        printf("Result: %d\n", result);
+    }
+    return 0;
+}
\ No newline at end of file
diff --git a/DS/C/Lab/Week5/PostfixToInfix.c b/DS/C/Lab/Week5/PostfixToInfix.c
new file mode 100644
index 0000000..b207c46
--- /dev/null
+++ b/DS/C/Lab/Week5/PostfixToInfix.c
@@ -0,0 +1,56 @@
+
+#include <stdio.h>
+#include <string.h>
+
+#define MAX_SIZE 100
+#define MAX_EXPR_LEN 200
+
+char stack[MAX_SIZE][MAX_EXPR_LEN];
+int top = -1;
+
+void push(const char* item) {
+    if (top >= MAX_SIZE - 1) {
+        printf("Stack Overflow\n");
+        return;
+    }
+    strcpy(stack[++top], item);
+}
+
+char* pop() {
+    if (top < 0) {
+        printf("Stack Underflow\n");
+        return NULL;
+    }
+    return stack[top--];
+}
+
+int isOperator(char c) {
+    return (c == '+' || c == '-' || c == '*' || c == '/' || c == '^');
+}
+
+void postfixToInfix(const char* postfix) {
+    char op1[MAX_EXPR_LEN], op2[MAX_EXPR_LEN], temp[MAX_EXPR_LEN];
+    
+    for (int i = 0; postfix[i] != '\0'; i++) {
+        if (!isOperator(postfix[i])) {
+            temp[0] = postfix[i];
+            temp[1] = '\0';
+            push(temp);
+        } else {
+            strcpy(op2, pop());
+            strcpy(op1, pop());
+            sprintf(temp, "(%s%c%s)", op1, postfix[i], op2);
+            push(temp);
+        }
+    }
+    
+    printf("Infix expression: %s\n", stack[top]);
+}
+
+int main() {
+    char postfix[MAX_SIZE];
+    printf("Enter postfix expression: ");
+    gets(postfix);
+    postfixToInfix(postfix);
+    return 0;
+}
\ No newline at end of file
diff --git a/DS/C/Lab/Week5/QueueStack.c b/DS/C/Lab/Week5/QueueStack.c
new file mode 100644
index 0000000..18fcab9
--- /dev/null
+++ b/DS/C/Lab/Week5/QueueStack.c
@@ -0,0 +1,84 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define MAX_SIZE 100
+
+typedef struct {
+    int items[MAX_SIZE];
+    int top;
+} Stack;
+
+Stack* createStack() {
+    Stack* s = (Stack*)malloc(sizeof(Stack));
+    s->top = -1;
+    return s;
+}
+
+void push(Stack* s, int x) {
+    if (s->top == MAX_SIZE - 1) {
+        printf("Stack Overflow\n");
+        return;
+    }
+    s->items[++(s->top)] = x;
+}
+
+int pop(Stack* s) {
+    if (s->top == -1) {
+        printf("Stack Underflow\n");
+        return -1;
+    }
+    return s->items[(s->top)--];
+}
+
+int isEmpty(Stack* s) {
+    return s->top == -1;
+}
+
+typedef struct {
+    Stack* s1;
+    Stack* s2;
+} Queue;
+
+Queue* createQueue() {
+    Queue* q = (Queue*)malloc(sizeof(Queue));
+    q->s1 = createStack();
+    q->s2 = createStack();
+    return q;
+}
+
+void enqueue(Queue* q, int x) {
+    push(q->s1, x);
+}
+
+int dequeue(Queue* q) {
+    int x;
+    if (isEmpty(q->s1) && isEmpty(q->s2)) {
+        printf("Queue is empty\n");
+        return -1;
+    }
+    if (isEmpty(q->s2)) {
+        while (!isEmpty(q->s1)) {
+            x = pop(q->s1);
+            push(q->s2, x);
+        }
+    }
+    return pop(q->s2);
+}
+
+int main() {
+    Queue* q = createQueue();
+    
+    enqueue(q, 1);
+    enqueue(q, 2);
+    enqueue(q, 3);
+    
+    printf("%d\n", dequeue(q));
+    printf("%d\n", dequeue(q));
+    
+    enqueue(q, 4);
+    
+    printf("%d\n", dequeue(q));
+    printf("%d\n", dequeue(q));
+    
+    return 0;
+}
\ No newline at end of file