First try

du3/program.c

@@ -0,0 +1,60 @@
+#include <stdio.h>
+#include<stdlib.h>
+#include <string.h>
+#include <assert.h>
+#define STACK_SIZE 10000
+
+struct stack{
+    float values[STACK_SIZE];
+    int size;
+};
+struct stack mystack;
+
+void push_stack(struct stack* stack, float value){
+assert(stack->size < STACK_SIZE); 
+stack->values[stack->size] = value;
+stack->size += 1;
+}
+float pop_stack(struct stack* stack){
+  assert(stack->size > 0);
+float value = stack->values[stack->size-1];
+stack->size -= 1;
+return value;
+}
+void print_stack(struct stack* stack){
+    for(int i = 0; i < stack->size; i++)
+        printf("%g ", stack->values[i]);
+    printf("\n");
+}
+  
+void process_operations(struct stack* stack){
+    char line[STACK_SIZE];
+    if(!fgets(line, STACK_SIZE, stdin)){
+        printf("Chyba\n");
+        return;
+    }
+    for(int i = 0; line[i] != '\0'; i++){
+        if(line[i] >= '0' && line[i] <= '9'){
+            char *endptr;
+            float val = strtof(&line[i], &endptr);
+            push_stack(stack, val);
+             print_stack(stack);
+            i = endptr - line - 1;
+        }
+        else if ((line[i] == '*' || line[i] == '+' || line[i] == '-' || line[i] == '/') 
+                  && stack->size >= 2){
+            float b = pop_stack(stack);
+            float a = pop_stack(stack);
+            float res = (line[i] == '+') ? a + b :
+                        (line[i] == '-') ? a - b :
+                        (line[i] == '*') ? a * b :
+                        (line[i] == '/') ? a / b : 0;
+            push_stack(stack, res);
+             print_stack(stack);
+        }
+    }
+}
+int main(void){
+    memset(&mystack,0,sizeof(struct stack));
+    process_operations(&mystack);
+}