create array 2 dimension decreasing

Question

here my code :

#include <stdio.h>
#define size 100

int main(){
    int a,b,i,j;
    int arr[size][size];
    
    
    printf("input : ");
    scanf("%d",&a);
    
    int a[a];
    
    arr[size][size]= a[a];
    for(i=0;i<a ;i++){
        a[i]=a[a]-a[i];
            for(j=0; j<i; j++){
                arr[i][j]=i+1/j+1;
            }
        
    }
    printf("%d", arr[i][j]);
    return 0;
}

I get problem and maybe someone want's to help me to fixed it. I confused in loop using decreasing and also array 2 dimension who not's print the true program.

this program should :

input :

5

output:

1.00 0.50 0.33 0.25 0.20
2.00 1.00 0.67 0.50
3.00 1.50 1.00
4.00 2.00
5.00

it's array using double or int?

Answer 1

• Declaring the array a after the integer a cause collision.
• The variable b is not used.
• You must not access arr[size][size] because it is out-of-range.
• double should be used to store floating-point number. (float may also work, but at least not int)
• To have value decrease, you can use subtraction.
• / operator has higher precedence than + operator, so you should use parenthesis to have it calculate + before /.
• Results of division between integers will be truncated. You should convert one of the operand to floating-pointe number before division.
• You should also put printing inside some loops.

Try this:

#include <stdio.h>
#define size 100

int main(){
    int a,i,j;
    double arr[size][size];
    
    
    printf("input : ");
    scanf("%d",&a);
    
    for(i=0;i<a ;i++){
            for(j=0; j<a-i; j++){
                arr[i][j]=(double)(i+1)/(j+1);
            }
        
    }
    for(i=0;i<a ;i++){
            for(j=0; j<a-i; j++){
                 printf("%.2f%c", arr[i][j], j+1<a-i ? ' ' : '\n');
            }
    }
    return 0;
}

Alternatively, you can avoid using floating-point number and use int for the array.

#include <stdio.h>
#define size 100

int main(){
    int a,i,j;
    int arr[size][size];
    
    
    printf("input : ");
    scanf("%d",&a);
    
    for(i=0;i<a ;i++){
            for(j=0; j<a-i; j++){
                arr[i][j]=(((i+1)*1000)/(j+1)+5)/10;
            }
        
    }
    for(i=0;i<a ;i++){
            for(j=0; j<a-i; j++){
                 printf("%d.%02d%c", arr[i][j]/100, arr[i][j]%100, j+1<a-i ? ' ' : '\n');
            }
    }
    return 0;
}

The formula (((i+1)*1000)/(j+1)+5)/10 is doing:

1. Calculate the division after multiplying 1000, so that it can calculate to 3 digit after the decimal point.
2. Add 5 and divide by 10 to round the result to 2 digits after the decimal point.