push operation fails in c stack data structure - c

Question

Hello everyone i got some issues here with the following code actually the code compiles successfully but when i called the display function it outputs one's instead of the actual content of the stack. can anyone explains to me what wrong with the display function.
thank you
#include <stdio.h>
#include <stdlib.h>
#define MAXSIZE 10
int stack[MAXSIZE];
int top = -1;
int menu();
void push();
void pop();
void peep();
void display();
void main() {
char ch;
int item;
do{
switch(menu()) {
case 1:
push();
break;
case 2:
pop();
break;
case 3:
peep();
break;
case 4:
display();
default:
printf("Invalid choice try again\n");
break;
}
printf("Do you want to continue ? (Y/N): ");
printf("top value is %d", top);
fflush(stdin);
scanf("%c", &ch);
}while(ch == 'Y' || ch == 'y');
}
int menu() {
int choice;
printf("Welcome to stack program \n\n");
printf("\n #1. push");
printf("\n #2. pop");
printf("\n #3. peep");
printf("\n #4. display");
printf("\nchoice: ");
scanf("%d", &choice);
return choice;
}
void push() {
int item;
printf("Enter element to add to stack: ");
item = scanf("%d", &item);
if(top == MAXSIZE - 1) {
printf("stack overflow can't add any more item\n");
exit(0);
} else {
top++;
stack[top] = item;
}
}
void pop() {
if(top == -1) {
printf("stack underflow deletion not possible\n");
exit(0);
} else {
printf("Element %d is deleted from the stack\n", stack[top]);
top--;
}
}
void peep() {
int i;
int element;
printf("Enter the location that you want to peep");
fflush(stdin);
scanf("%d", &i);
if(top - i + 1 < 0) {
printf("Location not valid");
exit(0);
} else {
element = stack[top - i + 1];
printf("The location %d contains the element %d \n", i, element);
}
}
void display() {
if(top != -1){
int j;
printf("Elements in the stack\n");
for(j = top; j >= 0; j--) {
printf("%d\n", stack[j]);
}
} else {
printf("Stack is empty\n");
}
}

Answer 1

Specific issues: missing break statement on case 4:; inconsistent use of fflush(stdin) when fpurge(stdin) seems to make more sense; using success exit code on failure and printing fatal errors to stdout instead of stderr; not clear what location in peep() represents relative to stack, should be documented;
I didn't like your basic design (all stack operations have void return value and no arguments) so I redid it such that the stack operations are functional and the I/O to get values into or out of them is handled external to the routines in the switch statement in main:
#include <stdio.h>
#include <stdlib.h>
#define MAXSIZE 10
int stack[MAXSIZE];
int top = -1;
int menu();
void push(int item);
int pop();
int peep(int location);
void display();
int main() {
char ch = 'Y';
int temporary;
while (ch == 'Y' || ch == 'y') {
switch(menu()) {
case 1:
printf("Enter element to add to stack: ");
(void) scanf("%d", &temporary);
(void) fpurge(stdin);
push(temporary);
break;
case 2:
temporary = pop();
printf("Element %d is deleted from the stack\n", temporary);
break;
case 3:
printf("Enter the location that you want to peep: ");
(void) scanf("%d", &temporary);
(void) fpurge(stdin);
printf("The location %d ", temporary);
temporary = peep(temporary);
printf("contains the element %d\n", temporary);
break;
case 4:
display();
break;
default:
printf("Invalid choice try again\n");
break;
}
printf("Value of 'top' is %d\n", top);
printf("Do you want to continue? (Y/N): ");
(void) scanf("%c", &ch);
(void) fpurge(stdin);
}
return EXIT_SUCCESS;
}
int menu() {
int choice;
printf("Welcome to stack program\n");
printf("\n #1. push");
printf("\n #2. pop");
printf("\n #3. peep");
printf("\n #4. display");
printf("\nchoice: ");
(void) scanf("%d", &choice);
(void) fpurge(stdin);
return choice;
}
void push(int item) {
if (top + 1 == MAXSIZE) {
fprintf(stderr, "stack overflow can't add any more item\n");
exit(EXIT_FAILURE);
}
stack[++top] = item;
}
int pop() {
if (top == -1) {
fprintf(stderr, "stack underflow deletion not possible\n");
exit(EXIT_FAILURE);
}
return stack[top--];
}
int peep(int location) {
if (top - location + 1 < 0) {
fprintf(stderr, "Location not valid");
exit(EXIT_FAILURE);
}
int element = stack[top - location + 1];
return element;
}
void display() {
if (top != -1) {
printf("Elements in the stack\n");
for (int j = top; j > -1; j--) {
printf("%d\n", stack[j]);
}
} else {
printf("Stack is empty\n");
}
}
Lots more error checking can, and should be done, this is not finished code.