Find the minimum number *homework*

**mariegrdnr** · 06-11-2014

Hello,
I am new this is my first post and was hoping someone may be able to direct me to my error, what I am asked to do,

Write a C program that takes multiple integers from the user and finds the minimum value. The numbers
entered by the user are positive integers. When the user is done entering all the numbers, the user enters
the sentinel value of -1.
This is a sample output. Notice how the program prints a counter (1, 2, 3, ) to help the user keep track of
how many numbers were entered so far. Include this feature in your program.

I have tried different ways to get the result from while loops, do while, and if-else statements. We have not done any max/min problem in class and the book was kind of vague. We have not learned arrays yet in class and I can't figure a way to compare the integers the user inputs as it is an infinite(from what I am reading) amount aloud. The problem I am seeing is the loop works and stops with the sentinel value but the INT_MIN is using the sentinel value. I also have not addressed the input of negative numbers yet with the first program I wrote, maybe one of my problems.
Thank You for any help,

Code:

/*File:HW2Q3.c, 
A C program that takes multiple integers from the user and finds the minimum
value. The numbers entered by the user are positive integers. When the user
is done entering all the numbers, the user enters the sentinel value of -1.*/
/*header files*/
#include<stdio.h>
#include<limits.h>
/*****start program*****/
int main()
{
    /*****declare variables*****/
    int a;//user input
    int counter=0;//counts entries
    INT_MIN;//for minimum value
    int sentinel;//program stops asking for input
    
    a=4;//initialize start value so while loop starts
    sentinel=-1;//initialize sentinel value
    INT_MIN != sentinel;/*****tried to use this statement to not
                 include -1 in minimum value (didn't work)*****/
     
    printf("Finding the minimum...\n");
    printf("Enter integers (-1 to finish)\n");             
    while(a!=-1)//start while loop to take user input and keep track of input
    {
                
                printf("%d integers: ",counter+1);//prints to screen
                scanf("%d",&a);//user input
                counter=counter + 1;//counts the entries from user
                
    /******I have tried this outside loop and same result as inside loop******/      
                if(a==-1)//start of if statement,(a) is compared to -1 print message
                printf("INT_MIN=%d\n",a);//prints minimum value entered
     
}//end while loop
    
        
              
system("pause");//pause program for user
return 0;//terminate program
}       //end main

I have also tried this way as well, min value still comes back as -1 the sentinel value, and the else statement is being ignored. I am sure it is something silly but I am lost and confused at this point.

Code:

  /*File:HW2Q3.c, 
A C program that takes multiple integers from the user and finds the minimum
value. The numbers entered by the user are positive integers. When the user
is done entering all the numbers, the user enters the sentinel value of -1.*/
/*header files*/
#include<stdio.h>
#include<limits.h>

/*****start program*****/
int main()
{
    /*****declare variables*****/
    
    int a;//user input
    int counter=0;//counts entries
    INT_MIN;//for minimum value
    
    
    a=4;
    if(a>=0)
    {
    
    while(a!=-1)//start while loop to take user input and keep track of input
    {
                
                printf("%d Enter numbers: ",counter+1);//prints to screen
                scanf("%d",&a);//user input
                counter=counter + 1;//counts the entries from user
                
                if(a==-1)
                printf("INT_MIN=%d\n",a);//prints minimum value entered
                          
                
}//end while loop
}
   
    else 
     {          
                printf("Use only positive numbers or enter -1 to finish input\n");
     } 
                           
              
system("pause");//pause program for user
return 0;//terminate program
}       //end main

**stahta01** · 06-11-2014

Please point to the line you declare the variable that is supposed to hold the minimum value entered.
What type is that variable?
What is that variable name?

Tim S.

**mariegrdnr** · 06-11-2014

OK I think what your asking is what I don't have? I have (int a) which I believe is holding the integers that the user is inputting then magically, I expect INT_MIN to pull the smallest number that was inputted. Type would be integer?

Code:

int a;//user input
INT_MIN;//for minimum value

printf("INT_MIN=%d\n",a);//prints minimum value entered

Sorry homework has gone past my understanding and I am struggling to keep up and understand what I am doing and why I am doing it. So you might have to be more blunt in what I need to look up urg sorry
Thank You,
Marie

**stahta01** · 06-11-2014

Why do you think this line will compile and what do you think it does?

Hint: It should NOT compile.

Code:

INT_MIN;//for minimum value

Tim S.

**mariegrdnr** · 06-11-2014

Ok I think that just tells you the size of the different types int, float, long long etc. lol, completely lost my mind

back to the book, I did say I was hoping it was a magically answer to my problem.
Thank You
marie

**anduril462** · 06-11-2014

You have identified your confusion with INT_MIN -- that's good. Another point to clarify, if you haven't figured it out yet, is this:

Code:

INT_MIN;

does nothing. It's like saying 42; Yes, there is a value associated with INT_MIN, but you don't store that value anywhere, nor do you make any decisions about the value (not part of a if condition or a loop condition). Similarly

Code:

INT_MIN != sentinel;

Is pointless. It does the comparison checking for INT_MIN not equal to sentinel, resulting in a true/false value. That value is never used though, so it's pointless. If you turn up the warning level on your compiler (-Wall option for GCC/MinGW, else you have to check your compiler docs) it should spit out a warning saying something like "foo.c:3: statement with no effect" -- that is, you have a pointless statement on line 3 of the file foo.c that you should fix or remove.

Sometimes it helps to read your code aloud in English or whatever your natural language is. Something like the following:

Code:

if(a==-1)
    printf("INT_MIN=%d\n",a);//prints minimum value entered

would sound like

If a is equal to -1, then print a as the minimum value entered

Do you see where the logic flaw is? You print the value of a, but you only do so when the if condition is true, i.e. when a is -1. Of course it always prints -1, since that's exactly what you told it to do

.

As for the second code example, where the else is being ignored, that's also simple. Only one of the if or the else can be executed. If the "if" condition is true, the if part is executed and the else part is ignored skipped. If the "if" condition is false, the if part is skipped and the else part is executed. So again, reading the following code aloud:

Code:

a = 4;
if (a >= 0)
{
    // do some stuff
}
else
{
    // do some other stuff
}

Sounds like: "Set a to 4. Compare a to 0. If a is greater than or equal to 0 (which it is, since 4 >= 0), then do some stuff. Otherwise, do some other stuff." See any logical flaw there? How can the else ever be executed?

I strongly suggest using clear, consistent indentation that accurately reflects the logical structure/flow of your program (see this link). It makes it much easier to follow the logic of your program.

Try working this out by hand, with paper and pencil. You can't program a computer to do a task, if you don't know how to do the task yourself. Imagine you are sitting down with your friend, and you are playing the part of the computer, while your friend says numbers to you. How would you keep track of the smallest number? How would you know when to stop? Pay careful attention to all the little steps you take, every time you check the value of a number, every you friend gives you a value that is the new minimum value. Write out every little step by hand on paper and pencil. Start in your native language. Then convert it to pseudo code, which resembles C code, but don't worry about syntax particulars, variable declarations, etc. Just get the logical structure correct. Then convert the pseudo code to C code, little by little, testing as you go. Start by just being able to read a list of numbers and stopping when you see your sentinel value. Then add the code for determining the minimum value entered (excluding the sentinel).

A couple more small pointers:

I prefer do-while loops for user input, since they always execute the body at least once, and you always want to ask the user for input at least once before doing anything.
Consider using a #define with a descriptive name for your sentinel value. It makes your code easier to read and modify. You can change the sentinel value by changing just one line (the #define) instead of many places.

**megafiddle** · 06-11-2014

Originally Posted by mariegrdnr

Ok I think that just tells you the size of the different types int, float, long long etc. lol, completely lost my mind

back to the book, I did say I was hoping it was a magically answer to my problem.
Thank You
marie

INT_MIN is the minimum (most negative) value that an int can hold. It's a predefined value (a C macro definition) and it's not going to be useful here.

You need to declare a variable to store the minimun value, eg, 'min'. You already have the input values stored in 'a', as the values are input.
Then all you need to do is compare 'a' to 'min' and assign 'min' a lower minimum value if a value lower than 'min' it is input. You do this inside
the loop that inputs the user values.

Also, since all the input values are positive integers, initialize 'min' to -1. When the first value of 'a' is input, 'min' will then start out as equal to 'a'.

Remember that a statement is only executed as it is encountered in a program. A statement that assigns a value will only do so when the statement
is encountered. The assignment will not happen automatically throughout the program.

-

**xrayextra** · 06-11-2014

Did your teacher teach you how to write an algorithm before writing code? It'd be VERY helpful here and for all future programming assignments.

**mariegrdnr** · 06-12-2014

Sorry it took so long, first thank you for all your help this is what I ended up with

Code:

/*File:HW2Q3.c, 
A C program that takes multiple integers from the user and finds the minimum
value. The numbers entered by the user are positive integers. When the user
is done entering all the numbers, the user enters the sentinel value of -1.*/
/*header files*/
#include<stdio.h>
/*****start program*****/
int main()
{
    /*****declare variables*****/
    int integer;//user input
    int counter=0;//counts entries
    int min;//minimum value
    int sentinel=-1;//sentinel value 
    
    min=10000;//declare min to anything other then sentinel
    printf("Finding the minimum...\n");//print message
    printf("Enter integers (-1 to finish)\n"); //print message 
    /*start while loop to take user input and keep track of input and stop if -1
    is entered*/  
         
    while(integer!=sentinel)//while loop runs loop til sentinel value is entered
    {
                
                printf("%d integers: ",counter+1);//prints counter to screen
                scanf("%d",&integer);//user input of integers
                counter=counter + 1;//counts the enteries from user 
                if(integer!=sentinel){//if statement so that it does not use sentinel value
                        if(integer<min){//if statement to compare new numbers entered
                        min=integer; //replace min with new number 
                         
                        }//closes integer<min if statement
                        }//closes integer!=sentinel if statement
     }//end while loop
      printf("The minimum integer entered= %d\n",min);//prints the min number         
system("pause");//pause program for user
return 0;//terminate program
}       //end main

if anyone has time let me know if there is statements that are not correct or garbage that may not be needed, I tried to make sure that all of it has a purpose and that I understand the purpose of the statement.
again thank you
marie

**mariegrdnr** · 06-12-2014

Originally Posted by xrayextra

Did your teacher teach you how to write an algorithm before writing code? It'd be VERY helpful here and for all future programming assignments.

summer class moving fast, he glossed over it with a couple examples, not his fault

garbage in garbage out up to me to pay closer attention and work harder

**anduril462** · 06-12-2014

Much, much better overall. First point to make, however, is that you should compile at the maximum warning level:

Code:

$ make foo
gcc -Wall -ggdb3 -pedantic -std=gnu99 -O0 -o foo foo.c -lm -lpthread -lrt
foo.c: In function ‘main’:
foo.c:36:5: warning: implicit declaration of function ‘system’ [-Wimplicit-function-declaration]

That means you didn't #include the header that defines the system() function. You need to add #include <stdlib.h> at the top of the file. It's worth noting that the pause command, which you run via the system() function, is Windows-specific. Thus, it causes an error message when I run your program on my Linux system. It's fine if you want or need to use it for class, just be aware that it is not portable.

Once you fix the #include, the algorithm works, but with one caveat: it only works if some numbers are smaller than 10000. If I enter 99999 and 10001 as my integers, your program will incorrectly report 10000 as the minimum entered integer. I suggest you use the constant INT_MAX provided by your implementation as the starting min value (it's the counterpart to INT_MIN, which you already know about). This way, no matter what int I enter, it will always be less than or equal to min, so if I only enter very large numbers, your program will still work. Make sure you #include <limits.h> to have access to it. Use INT_MAX for your starting min value.

Your variable names are much better, and you have comments that explain the code, which makes it easier to read, understand and maintain, which are very important features of any software project. Your indentation is still a bit lacking, but some of that may be from copy-pasting into the forum. Using only spaces for indenting, instead of tab or a mix of spaces and tabs, usually helps with this.

You do have too many comments, however. This is not unusual when you are new, either because it is a requirement for the assignments (to ensure students do write some comments), or it helps you understand what you are doing. However, in general, you don't want to comment every line. Definitely don't comment the obvious, like "// print message". You should strive to write clear, easily-understood code that is as "self-documenting" as possible. Good variable/function/type names, and small functions with clear logic and structure take care of much of that. Comments should only be used to explain code that is not obvious, for example: how a complicated algorithm works; why you are doing something the way you are, like choosing an awkward/non-intuitive way of doing something to avoid a bug in the implementation (unlikely, but I've seen it happen).

**mariegrdnr** · 06-12-2014