Program to print value of array using for loop

Question

i want to create this simple program using for loop. Now what it should do is get a value from an array and print it corresponding to the day(1-30).

Here is my code.

#include<stdio.h>

int main() {

    int j;
    int days=1;
    int value[]={31,30,29,28,27,26,25,24,23,22,21,20,19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1};
    
    for(days=1; days<=31; days++){
        
            for(j=value[0]; j<=value[].length; j++){
                printf("%d \t %d\n", days, j);  
            }
        
        
        }
}

when i run this the value[] doesnt change... i believe im having trouble incrementing the index of array...

somebody help... how do i do it???

Answer 1

First of all, value[].length] is not permissible in C to determine the length of an array. As side note there is also an abandoned ] after length which would give you a syntax error, even if you would use a C++ compiler to compile this code.

If you want to get the amount of elements you need to use f.e. the sizeof operator and divide the amount of allocated memory in bytes by the memory per element object:

sizeof(value) / sizeof(value[0])

Furthermore the algorithm of the inner for loop

j = value[0]; j <= value[].length; j++){

makes no sense. Why would you want to compare the value at a certain array element with the length of the whole entire array instead of to iterate over the array until the matched value is found?

Think about what you are doing!

You also need another if check to proof it you encountered the right value.

For example:

#include <stdio.h>

int main (void) {

    unsigned int j;
    unsigned int days = 1;
    unsigned int value[] = { 
                             31,30,29,28,27,26,
                             25,24,23,22,21,20,
                             19,18,17,16,15,14,
                             13,12,11,10,9,8,7,
                             6,5,4,3,2,1
                           };

    unsigned int len = sizeof(value) / sizeof(value[0]);

    printf("Day \t Index \t Value\n");
    
    for (days = 1; days <= 31; days++) {
         for (j = 0; j < len ; j++) {
              if (value[j] == days)
                   printf("%u \t %u \t %u\n", days, j, days);  
         }        
    }
}

Output:

Day   Index  Value
1     30     1
2     29     2
3     28     3
4     27     4
5     26     5
6     25     6
7     24     7
8     23     8
9     22     9
10    21     10
11    20     11
12    19     12
13    18     13
14    17     14
15    16     15
16    15     16
17    14     17
18    13     18
19    12     19
20    11     20
21    10     21
22    9      22
23    8      23
24    7      24
25    6      25
26    5      26
27    4      27
28    3      28
29    2      29
30    1      30
31    0      31

---

Side Notes:

• I used unsigned int because it is unusual that you have negative days and it is better for the comparison with the return of the sizeof operation to determine the length of the array value.

• The formatting of the output can be different on your implementation because how many spaces \t is exactly, is implementation-specific.

• Use a C compiler to compile C code and never ignore compiler warnings. Don't intermix C with C++ code.

• Use int main(void) instead of int main(). The latter is not strict C standard-compliant.

• Good and free C starting books are Modern C or The C Programming Language (2nd Edition). These and others you can find here:

  The Definitive C Book Guide and List

Answer 2

Alright. I haven't really done anything such like what you are wanting to do.
But, my understanding is, for day one you would want to print 31..
Here is what I did to refactor it:

#include<stdio.h>

int main() {

    int j;
    int days=1;
    int value[]={31,30,29,28,27,26,25,24,23,22,21,20,19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1};
    
    for(days=1; days<=31; days++){
        
            for(j=1; j<=value[days]; j++){
                printf("%d \t %d\n", days, j);
            }
        
        
        }
}

It is kinda hard to figure a day as a number when you are giving the for loop 0-31...

I hope this somewhat helps you out..

Answer 3

As your data size is pretty large, I would suggest using a for loop to generate each day and then store them to an array as the for loop runs. You can print each day at the end of each loop. Here is how you can do it differently:

#include<stdio.h>

int main()
{
    int dayCount;
    int days = 31; //if you already knew you want to print days 1 - 31, might as well initiate the array size

    int value[days];
    int arrayCount;

    //assigning days 1 - 31 into the array
    for(dayCount = 1 ; dayCount <= 31 ; dayCount++)
    {
        value[dayCount] = dayCount;
        //you can also choose to print the element of the array here as the loop runs
    }

    //to print all elements of the array
    for(arrayCount = 1 ; arrayCount < days ; arrayCount++)
    {
        printf("Index: %d \tDay: %d\n", arrayCount, value[arrayCount]);
    }
}

However, this is only enough if you want to be rigid and strictly print days 1 - 31. If you have robustness in mind, best check out the answer from "RobertS supports Monica Cellio".