Question

1. In C Programing Create a stack using an array. Define the index variable of the array name to be stacktop. Initially set stacktop to -1. Next create two functions push and pop. Both take as input 3 items: a pointer to the stack in memory, stacktop, and maxstack.
2. Make sure to inc stacktop by one and also remember that stacktop[0] is the bottom of the stack and by stack rule cannot be accessed until all the other items are popped.
3. Your program should push and pop values between 1 and 1000 until a negative input is encountered. When the program incurs a negative number, it should pop all remaining stack items until the stack is empty
4. Next change the data field in the program to be char type. Then push the letters of your name one at a time. When you have finished entering them, pop each one off and print them. You will see that this demonstrates the reversing effect of a stack.

Answer 1

C program with int data field of stack (for inputs from 1 - 1000):

#include <stdio.h>
#define MAX_LEN 100   //it is the max length of the stack 


//function to push elements to stack
//parameters: stack array, value to be pushed, pointer to stack top
//return: void
void push (int *stack, int value, int *stackTop){

    ///if the stack is full
    if (*stackTop == MAX_LEN) {
        printf("Stack is full.\n\n");
        return ;
    }

    //increment the top of the stack
    *stackTop = *stackTop +1;

    //push the new value to stack
    stack[*stackTop] = value; 
    printf("Pushed %d to stack\n\n", value);

}


//function to pop elements from stack
//parameters: stack array,  pointer to stack top
//return: popped element
int pop (int *stack, int *stackTop) {

    //if stack is empty
    if ( *stackTop == -1) {
        printf("Stack is Empty\n\n");
        return -1 ;
    }


     int temp = stack[*stackTop] ;
    
    //decrement the top of the stack
     *stackTop = *stackTop -1;

     //return the popped element
     return temp ;

}

int main(){
   
  int stack[5000];
  int stackTop = -1 ;
  int input = 0 ;
  

  //take continuous input from user until a negative number is entered
  while(1){
    printf("1) PUSH \n2) POP \nChoose an option to perform your task: ");
    int op;
    scanf("%d", &op);

    //push
    if (op == 1) { 
        printf("Enter a number between 1 - 1000 (inclusive): ") ;
        scanf("%d", &input) ;

        //check is eneterd value is valid
        if ( input >0 && input < 1001) {
            push(stack, input, &stackTop);
        }

        //if its is negative
        else if(input < 0) break;
        //if its positive but out of range
        else {
            printf("Error: Number should be between 1 to 1000 (inclusive) \n\n");
        }
    }
    //pop
    else if (op == 2) { 
        int popped_elem = pop(stack, &stackTop);
        if(popped_elem != -1){
            printf("Popped %d from stack\n\n", popped_elem);
        }
    }
    
    else {
        printf("Invalid Choice. \n\n");
    }
  }
 
 printf("You entered a negative number\nPoppping all elements from stack:\n");

 //popping all elements from stack
 while(stackTop > -1){
     int popped_elem = pop(stack, &stackTop);
     printf("%d\n", popped_elem);
 }
printf("Now stack is empty!!\n");
}

Output:

C program with char data field of stack (for inputing your Name):

#include <stdio.h>
#define MAX_LEN 100  //it is the max length of the stack 

//function to push elements to stack
//parameters: stack array, value to be pushed, pointer to stack top
//return: void
void push (char *stack, char value, int *stackTop){

    // if stack is full 
    if (*stackTop == MAX_LEN) {
        printf("Stack is full.\n\n");
        return ;
    }
 
  //increment the top of the stack
    *stackTop = *stackTop +1;
    stack[*stackTop] = value; 
    printf("Pushed %c to stack\n\n", value);

}

//function to pop elements from stack
//parameters: stack array,  pointer to stack top
//return: popped element
char pop (char *stack, int *stackTop) {

     //if stack is empty
    if ( *stackTop == -1) {
        printf("Stack is Empty\n\n");
        return '\0';
    }
     char temp = stack[*stackTop] ;

     //decrement the top of the stack
     *stackTop = *stackTop -1;

     //return the popped element
     return temp ;

}

int main(){
   
  char stack[5000];
  int stackTop = -1 ;
  char input ;


//take continuous input from user until a negative number is entered
  while(1){
    printf("1) PUSH \n2) POP \nChoose an option to perform your task: ");
    int op;
    scanf("%d", &op);
    getchar();

    //push
    if (op == 1) { 
        printf("Enter a character(alphabet): ") ;
        scanf("%c", &input) ;
        
       // check if the input is an alphabet
        if ( (input >= 65 && input < 91) || (input >= 97 && input < 123)) {
            push(stack, input, &stackTop);
        }

        // if it is not an alphabet break the loop
        else  break;
    }
   // POP
    else if (op == 2) { 
        char popped_elem = pop(stack, &stackTop);
        if(popped_elem != '\0'){
            printf("Popped %c from stack\n\n", popped_elem);
        }
    }
    
    else {
        printf("Invalid Choice. \n\n");
    }
  }
 
 printf("You entered a n invalid character\nPoppping all elements from stack:\n");
 //popping all elements from stack
 while(stackTop > -1){
     char popped_elem = pop(stack, &stackTop);
     printf("%c\n", popped_elem);
 }
printf("Now stack is empty!!\n");
}

OUTPUT:

if you find this solution helpful, do upvote as it motivates me to post more answers.