View difference between Paste ID: JFzdin6h and A6upR5xW

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
 
 #define STACKSIZE 250
 
 typedef struct{
         int top;
         long long int items[STACKSIZE];
         }STACK;
 
 
 void push(long long int x, STACK *ps);
 int pop(STACK *ps);
 int ispositivedigit(char* input);
 int isnegativedigit(char* input);  // function for detection negative numbers
 void printtop(STACK *ps);  // bonus
 
 
 
 int main()
 {
     char input[1024];  // array for loaded values
 
     int end = 1;  // detects end of input
     int count = 0;  // variable for detection if no arguments were enetred
     STACK ps = {0, {0}};
     long long int number, a, b, result, printresult;
 
 
     while (end != EOF) {
 
         // Read next token
         end = scanf("%s", input);
         count += 1;
         if(end == EOF) {
             count -= 1;
             break;
         }
 
         // If it's a numebr
-        if (ispositivedigit(input) || isnegativedigit(input)) {
+        if (ispositivedigit(input) == 1 || isnegativedigit(input) == 1) {
             number = atoll(input);  // converts string to long long int
             push(number, &ps);  // add a number to the top of the stack
         }
         // It it's an operator
-        else if (isoperator(input)) {
+        else if (isoperator(input) == 1) {
             // p
             if (strcmp(input, "p") == 0) {
                 printtop(&ps);
             }
             // +
             else if (strcmp(input, "+") == 0) {
                 a=pop(&ps); b=pop(&ps);
                 result = a + b;
                 push(result, &ps);
             }
             // -
             else if (strcmp(input, "-") == 0) {
                 a=pop(&ps); b=pop(&ps);
                 result = a - b;
                 push(result, &ps);
             }
             // *
             else if (strcmp(input, "*") == 0) {
                 a=pop(&ps); b=pop(&ps);
                 result = a * b;
                 push(result, &ps);
             }
             // /
             else if (strcmp(input, "/") == 0) {
                 a=pop(&ps); b=pop(&ps);
 
                 if (a == 0) {
                     fprintf(stderr, "Error: Division by zero!\n");
                     exit(EXIT_FAILURE);
                 }
                 else result = b / a;
 
                 push(result, &ps);
             }
         }
         // Detect invalid input
         else {
             fprintf(stderr, "Error: Invalid input!\n");
             exit(EXIT_FAILURE);
         }
     }
 
     // Returns error when no arguments are entered
     if (count == 0) {
         fprintf(stderr, "Error: No arguments!\n");
         exit(EXIT_FAILURE);
     }
 
 
     // If the last character isn't "p", the program print the result clasically
     if (strcmp(input, "p") != 0) {
         printresult = pop(&ps);
         printf("%lld\n", printresult);
     }
 
     return 0;
 }
 
 
 
 void push(long long int x, STACK *ps)
 {
     if (ps->top == STACKSIZE-1){
         fprintf(stderr, "Error: Stack overflow!\n");
         exit(EXIT_FAILURE);
     } else
         ps->items[++(ps->top)] = x;
 
     return;
 }
 
 
 
 int pop(STACK *ps)
 {
     if (ps->top == 0) {
         fprintf(stderr, "Error: Stack underflow!\n");
         exit(EXIT_FAILURE);
     }
     else
         return(ps->items[(ps->top)--]);
 }
 
 
 
-bool ispositivedigit(char* input)
+int ispositivedigit(char* input)
 {
     // cycle which determines if each character from input is a number or not
     for (unsigned int i=0; i<strlen(input); i++) {
         if (isdigit(input[i]) == 0) {}
-            return false;
+            return 0;
         }
     }
 
-    return true;
+    return 1;
 }
 
 
 
-bool isnegativedigit(char* input)
+int isnegativedigit(char* input)
 {
     if (strlen(input) > 1 && strncmp(input, "-", 1) == 0) {
         for (unsigned int i = 1; i < strlen(input); i++) {
             if (isdigit(input[i]) == 0) {
-                return false;  // if a character different from number appears, function returns false
+                return 0;  // if a character different from number appears, function returns 0
             }
         }
     }
     else
-        return false;  // if the firts character isn't "-", function returns false
+        return 0;  // if the firts character isn't "-", function returns 0
 
-    return true;  // it is a negative number
+    return 1;  // it is a negative number
 }
 
 
 
-bool isoperator(char* input)
+int isoperator(char* input)
 {
-    if (strlen(input) != 1) return false;  // only one-char operators are allowed
+    if (strlen(input) != 1) return 0;  // only one-char operators are allowed
 
-    if (strncmp(input, "+", 1) == 0) return true;
+    if (strncmp(input, "+", 1) == 0) return 1;
-    if (strncmp(input, "-", 1) == 0) return true;
+    if (strncmp(input, "-", 1) == 0) return 1;
-    if (strncmp(input, "*", 1) == 0) return true;
+    if (strncmp(input, "*", 1) == 0) return 1;
-    if (strncmp(input, "/", 1) == 0) return true;
+    if (strncmp(input, "/", 1) == 0) return 1;
-    if (strncmp(input, "p", 1) == 0) return true;
+    if (strncmp(input, "p", 1) == 0) return 1;
 
-    return false;
+
 }
 
 
 
 void printtop(STACK *ps)  // bonus
 {
     // not empty stuck
     if (ps->top != 0)
         printf("%lld \n", ps->items[ps->top]);
     // empty stack
     else {
         fprintf(stderr, "Error: Attempt to call for an empty stack!\n");
         exit(EXIT_FAILURE);
     }
 }