Using C to Find Min and Max value using Function

Question

I need to write a program where users can input their numbers as much as many as they defined, then the program will try to find which one is the lowest value and the highest value. The problems I face are:

1. When the program executed, the second line will wait on user's input (number) before the printf
2. The error "system" seems unreliable, sometimes works, sometimes doesn't work
3. The program only checks the last number entry, therefore it only shows the last number in min and max

You may give hints or corrections along the answers. Thank you very much.

#include <stdio.h>
float max(float num1){
    float a=0, b;
        if(num1 > a){
            a=num1;
        }
    return a;
}

float min(float num2){
    float x=100, y;

        if(num2 < x ){
            x=num2;
        }

    return num2;
}

int main(){
    int times, interval;
    float mini, maxi, data_Input;

    printf("How many number would you like to type in ? : ");
    scanf("%d\n",&times);

    printf("Type in the number: ");
    scanf("%f", &data_Input);

    for(interval=2; interval<=times; interval++){
        printf("\nType in the number: ");
        scanf("%f",&data_Input);
        while(data_Input<0){
            printf("Invalid Input! Please re-enter the number:");
            scanf("%f",&data_Input);
        }
        while(data_Input>100){
            printf("Invalid Input! Please re-enter the number:");
            scanf("%f",&data_Input);
        }
    
    }
    maxi= max(data_Input);
    mini= min(data_Input);

    printf("The Lowest Number is %.2f\n", mini);
    printf("The Highest Number is %.2f\n", maxi);
    return 0;
}

Output:

How many number would you like to type in? : 5
70
Type in the number : 
Type in the number : 90.7
Type in the number : 99
Type in the number : 30
Type in the number : 50
The Lowest Number is 50.00
The Highest Number is 50.00

Answer 1

Okay, the thing is that you are not updating the data_input after every successive number is inputted. What you are doing is, comparing the last number to 0 or 100, which is logically incorrect. How about you take the first number as input, then after every successive input, compare it with the min and max value. Here is the sample code.

#include <stdio.h>
float max(float num1, float num2){
    if(num1 > num2){
        return num1;
    }
    return num2;
}

float min(float num1, float num2){
    if(num1 < num2){
        return num1;
    }
    return num2;
}

int main(){
    int times, interval;
    float mini, maxi, data_Input;

    printf("How many number would you like to type in ? : ");
    scanf("%d\n",&times);

    printf("Type in the number: ");
    scanf("%f", &data_Input);
    
    // the first number will be minimum and maximum
    mini = data_Input;
    maxi = data_Input;

    for(interval=2; interval<=times; interval++){
        printf("\nType in the number: ");
        scanf("%f",&data_Input);
        // make it a composite if condition
        while(data_Input<0 || data_Input>100){
            printf("Invalid Input! Please re-enter the number:");
            scanf("%f",&data_Input);
        }
        maxi= max(maxi, data_Input);
        mini= min(mini, data_Input);
    
    }
    

    printf("The Lowest Number is %.2f\n", mini);
    printf("The Highest Number is %.2f\n", maxi);
    return 0;
}

Answer 2

The program checks the last number because you are calling the min and max function out of the for bracelets so instead you can call them inside the for bracelets like:

for(interval=2; interval<=times; interval++){
        printf("\nType in the number: ");
        scanf("%f",&data_Input);
        while(data_Input<0){
            printf("Invalid Input! Please re-enter the number:");
            scanf("%f",&data_Input);
        }
        while(data_Input>100){
            printf("Invalid Input! Please re-enter the number:");
            scanf("%f",&data_Input);
        }
        maxi= max(data_Input);
        mini= min(data_Input);
    }

and instead of rewriting the same code you can just ask for the numbers inside the for loop and to initialize your interval to 1 so your main will look like:

int main(){
    int times, interval;
    float mini, maxi, data_Input;

    printf("How many number would you like to type in ? : ");
    scanf("%d\n",&times);

    for(interval=1; interval<=times; interval++){
        printf("\nType in the number: ");
        scanf("%f",&data_Input);
        while(data_Input<0){
            printf("Invalid Input! Please re-enter the number:");
            scanf("%f",&data_Input);
        }
        while(data_Input>100){
            printf("Invalid Input! Please re-enter the number:");
            scanf("%f",&data_Input);
        }
        maxi= max(data_Input);
        mini= min(data_Input);
    }

    printf("The Lowest Number is %.2f\n", mini);
    printf("The Highest Number is %.2f\n", maxi);
    return 0;
}

Answer 3

Solving the printf issue is easy. As stdout is line buffered (at least by default - it can be changed) it is flushed whenever a newline is inserted in the buffer. So, just add a newline after each message print, for example

printf("How many number would you like to type in ? : \n");

and you'll be fine.

---

Talking about the wrong calculation of min and max, your attempt has basically two big issues:

• You are not acquiring times inputs, but only one. In fact, every time you call scanf you overwrite the same variable data_Input without performing any comparison with the previous inputs
• You call min() and max() function only once, after the last input. Furthermore you try to compare the argument with a local variable that has local storage and a lifetime limited to the function itself so that at the next call it will be initialized again

In order to have a variable inside a function that it is initialized only the first time you can use static keyword. But it is not I suggest you to solve the issue.

In my opinion you don't need comparison functions: you can just update maxi and mini each time you get a new input (solving both the aforementioned issues at once):

int main(){
    int times, interval;
    float mini, maxi, data_Input;

    printf("How many number would you like to type in ? : \n");
    scanf("%d",&times);

    printf("Type in the number: ");
    scanf("%f", &data_Input);

    maxi = data_Input;
    mini = data_Input;

    for(interval=2; interval<=times; interval++){
        printf("\nType in the number: \n");
        scanf("%f",&data_Input);
        while(data_Input<0){
            printf("Invalid Input! Please re-enter the number:\n");
            scanf("%f",&data_Input);
        }
        while(data_Input>100){
            printf("Invalid Input! Please re-enter the number:\n");
            scanf("%f",&data_Input);
        }
        
        /* Check input and, in case, update max and min */
        if(data_Input > maxi)
             maxi = data_Input;

        if(data_Input < mini)
             mini = data_Input;
    }

    printf("The Lowest Number is %.2f\n", mini);
    printf("The Highest Number is %.2f\n", maxi);
    return 0;
}

The comparison is performed inside the loop, so you don't need to store the inputs into an array.

Answer 4

You have plenty issues in your code.

1. Functions min & max do not make any sense
2. You do not check result of the scanf and you do not know if it was successfull

#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define MIN(a, b) ((a) < (b) ? (a) : (b))

int main()
{
    int times, interval;
    float mini, maxi, data_Input;

    do 
    {
        printf("\nHow many number would you like to type in ? : ");
    }while(scanf(" %d\n",&times) != 1);

    for(interval = 0; interval < times; interval++)
    {
        do 
        {
            printf("\nType in the number: ");
        }while(scanf(" %f",&data_Input) != 1 && (data_Input < 0 || data_Input > 100));

        printf("%f\n", data_Input);

        maxi = interval == 0 ? data_Input : MAX(maxi, data_Input);
        mini = interval == 0 ? data_Input : MIN(mini, data_Input);
    
    }
    printf("The Lowest Number is %.2f\n", mini);
    printf("The Highest Number is %.2f\n", maxi);
    return 0;
}

Answer 5

When the program executed, the second line will wait on user's input (number) before the printf

Drop "\n" from "%d\n". It blocks until non-white space detected after the number and is not needed.

printf("How many number would you like to type in ? : ");
// scanf("%d\n",&times);
scanf("%d",&times);
printf("Type in the number: ");

If output still not seen when expected, flush it. Typically printing a '\n' will flush stdout, but not certainly.

printf("How many number would you like to type in ? : ");
fflush(stdout);  // add

---

The error "system" seems unreliable, sometimes works, sometimes doesn't work

At least this issue: sequential check vs. checking both conditions together input validity.

Rather than

    while(data_Input<0){
      ...
    }
    while(data_Input>100){
      ...
    }

Test together.

    while(data_Input<0 || data_Input>100){
      ...
    }

---

The program only checks the last number entry, therefore it only shows the last number in min and max

True as code only compares values once with one call to max(). That function only compares the number to 0 rather than prior values. Likewise for min().

Consider an algorithm change

// Pseudo code for max
prompt How many number would you like to type in ? : "
get times

max_value = -INF // set to minimum possible float

for each value 1 to times
  prompt "Type in the number: "
  get data_Input
  if  data_Input > max_value
    max_value = data_Input

print max_value