how can i improve/reduce this code? [closed]

The most immediate observation is:

• When you see code like:

  int ... p1, p2, p3, p4, p5, p6, p7, p8, ...;
  

  you should immediately think 'array'.

• When you see code like:

  p1=rand()%1201+500;
  p2=rand()%2101+1500;
  p3=rand()%7001+5000;
  p4=rand()%5501+3500;
  p5=rand()%12001+8000;
  p6=rand()%30001+15000;
  p7=rand()%70001+40000;
  p8=rand()%65001+35000;
  

  you should immediately be thinking 'array of structures'.

• You should also worry about those modulo operations. The range of values returned by rand() is denoted RAND_MAX and might be as small as 32767, in which case your modulo operations for p7 and p8 are not doing anything. Actually, you should revisit the random number generation altogether. You should probably be using something like (rand() / (double) RAND_MAX) * max_value to get a value between 0 and the maximum value (such as 7001).

• When you see code like:

   printf("Item                   On hand                 Price\n");
   printf("\n");
   printf("Phoenix Down              %d                    %dG\n", on, p1);
   printf("Elixir Essence            %d                    %dG                 Day   #%d\n",on, p2, d);
   printf("Platinum Ingot            %d                    %dG                 Gil:%d\n",   on, p3, g);
   printf("Golden Materia            %d                    %dG                 Debt:%d\n", on, p4, de);
   printf("Scarlette                 %d                    %dG\n",on, p5);
   printf("Adamintite                %d                    %dG\n",on, p6);
   printf("Dark Matter               %d                    %dG\n",on, p7);
   printf("Trapezohedron             %d                    %dG\n",on, p8);
   printf("\n");
   printf("[1]Buy  [2]Sell  [3]eave\n");
   printf("\n");
   printf("Option: ", option);
   scanf("%d", &option);
   if(option == 1)
   {
   system("cls");
   printf("************************\n");
   printf("Tycoon Meteor's Minerals\n");
   printf("************************\n");
   printf("\n");
   printf("Shopkeeper: Buying an item? Which one?\n");
   printf("\n");
   printf("Item                       On hand                Price\n");
   printf("\n");
   printf("[1]Phoenix Down              %d                    %dG\n", on, p1);
   printf("[2]Elixir Essence            %d                    %dG            Day# %d\n",on, p2, d);
   printf("[3]Platinum Ingot            %d                    %dG            Gil:%d\n", on, p3, g);
   printf("[4]Golden Materia            %d                    %dG            Debt:%d\n", on, p4, de);
   printf("[5]Scarlette                 %d                    %dG\n",on, p5);
   printf("[6]Adamintite                %d                    %dG\n",on, p6);
   printf("[7]Dark Matter               %d                    %dG\n",on, p7);
   printf("[8]Trapezohedron             %d                    %dG\n",on, p8);
   printf("\n");
  

  with its vast block of repeated material, you should be thinking 'subroutine'. Actually, probably several subroutines. The repetition is a maintenance nightmare. Yes, handling the special cases for items 2, 3, and 4 complicates life a little. Yes, deciding whether to output the [1] before the item name complicates it a little. You should probably be using %6d or something similar for the 'quantity on hand', and quite likely for the price too.

• It is a little surprising that you have the same number on of each item available. Are you sure that shouldn't be calculated (generated at random) too?

• Of course, the functions will need arguments to define what to print, etc. But you really need to use some basic structures.

In the code:

printf("Your Choice: ", Choice);
scanf("%d", &Choice);
switch (Choice)
{
case 1:
    Tycoons(&g,&on,&d,&de);
    break;
case 'q':
    printf("Thank you for playing!");
    exit(0);
    break;
}

• Your printf() format doesn't need the argument Choice.
• You scan for an integer.
• You do not check that scanf() was successful.
• Your switch requires your users to know that the code for 'q' is 113.
• Your switch needs a default clause to catch the 'any other response'.

We could get into a philosophical debate about the merits or otherwise of scanf(). Suffice to say that it is hard to use correctly and harder still to recover from errors when using scanf(). If you're going to be reading single characters without the user having to hit return after each choice, then you should probably not be using scanf(). If you're going to want answers with a newline at the end of each, you'd probably do better reading the input with fgets() and then using sscanf() to parse the data that was read. Of course, ultimately, you'll need a function that handles the input—that handles a prompt, recognizes when the data is bad, reprompts, handles EOF (exit game?), etc.

Choice = prompt("Your choice: ", "12345678q");

The function is given the prompt string and a list of valid options (here, 8 digits for 8 emporia plus 'q' for quit). The value in Choice is probably the character code, so the cases in the switch become (note the single quotes):

case '1':
    Tycoons(&g,&on,&d,&de);
    break;

but your input code is reading a character, not a number (so "%d" is not the correct format) and returns the number corresponding to the character entered.