CODEWITHSUNDEEP
c
George Papatheodorou
George Papatheodorou

Reputation: 1559

Unusuall way to fill multiple rows in an array non recursively?

Hi I m debugging a C app and seing this strange behavior in an array of 10 rows and 4 columns:

void fillArray(int *B){ 
 //DEBUG
    printArray(B,10,4);//printing all items 0's
    B[3,0] =  3;
    printArray(B,10,4); // results in B[0,0] = 3 , B[1,0] = 3 , B[2,0] = 3  , B[3,0]= 3 , ...
                    // Rest values remains zero.
}



 void printArray(int *B,int imax,int jmax){
     printf(" \n --- Check---");    

    for(i=0;i<imax;i++){
        for(j=0;j<jmax;j++){            
            printf(" \n Check: B[%d,%d]=%d ",i,j,B[i,j]);
        }
    }    
}

Why does value 3 is inserted in every row of the table for column 0 ?

Upvotes: 0

Views: 46

Answers (3)

Iharob Al Asimi
Iharob Al Asimi

Reputation: 53016

Because the , operator discards all the operands except the last. So this

B[3,0] = 3;

is effectively

B[0] = 3;

and how many columns does your table have? since it's an int * I doubt that you have a table. The suggested syntax

B[3][0] = 3;

is wrong too, because B[3] has type int and you cannot index an int.

Upvotes: 0

md5
md5

Reputation: 23717

In C, the syntax for two-dimensional arrays is:

B[3][0] = 3

rather than:

B[3,0] =  3;`

, is the comma operator which has an other meaning (basically, the value of the expression a, b is b).

Upvotes: 1

Vatine
Vatine

Reputation: 21288

You're using the expression 3, 0 to index the array. That expression has the value 0 (it's using the sequence operator, the value of which is the value of the last expression, in this cas e a constant 0). To index a multi-dimensional array in C, you need to use something like m[a][b].

Upvotes: 1

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