I can't seem to fix this issue about nested for loops + 2d arrays

Rahim Medjber 0
Viewed 36

this is the code I am having a problem with 1 2 the code:

#include <stdio.h>
#include <stdlib.h>


int main(){ 

    int i, j;
    int num[3][2] = { (1, 2),
                      (3, 4),
                      (5, 6)
                    };
    for(j = 0; j < 3; j++){
        for( i = 0; i < 2; i++ ){
            printf("%d, ", num[j][i]);
        }   printf("\n");
    }
    return 0;
}

guys I am watching this course of freecodecamp about the C language and the guy tutoring got this code right as it says in the console: 1, 2, 3, 4, 5, 6, and I typed the EXACT same code but still not working, I double- checked and everything, but nothing seems to work. 3

nested-loops multidimensional-array c
2 Answers

As @Oka said you need to use {} in the initializer. Also fixing formatting, separators, and localizing variables:

#include <stdio.h>
#include <stdlib.h>

int main() {
    int num[3][2] = {
        {1, 2},
        {3, 4},
        {5, 6}
    };
    for(size_t j = 0; j < sizeof(num) / sizeof(*num); j++) {
        for(size_t i = 0; i < sizeof(*num) / sizeof(**num); i++ ) {
            printf("%d%s",
                num[j][i],
                i + 1 < sizeof(*num) / sizeof(**num) ? ", " : "\n"
            );
        }
    }
    return 0;
}
Allan Wind0

Both @Oka and @Allan Wind have written that you've used () where {} is the correct way to define data in an array.

Below uses a different layout for the small amount of data being specified.

It also shows (similar @Allan's answer) how to let the compiler measure the array's dimensions, uses those values as limits to the loops. The compiler "knows" there are 3 rows (better than erring humans could do.) If a 4th row is added, re-compiling will use the right value without the programmer remembering to change the loop counter from 3 to 4.

This version uses fewer {} in the code, certain that there is only one executable statement properly indented. This alternative style is more compact and less garish.

As nice as they are, i & j are overused and, therefore, meaningless. Notice the use of r & c that hints at being row & col. Easier to keep things straight when variable names suggest their meaning and use.

Notice how the indentation in the two versions highlights when printf( "\n" ); will be executed. Whitespace is important for readability. Respect it.

#include <stdio.h> // don't include what you don't need

int main() {
    int r, c, num[][2] = { { 1, 2 }, { 3, 4 }, { 5, 6 } };
    int nRows = sizeof num/sizeof num[0];
    int nCols = sizeof num[0]/sizeof num[0][0];

    printf( "Version 1:\n" );
    for( r = 0; r < nRows; r++ ) {
        for( c = 0; c < nCols; c++ )
            printf( "%d, ", num[ r ][ c ] );
        printf( "\n" );
    }

    printf( "\nVersion 2:\n" );
    for( r = 0; r < nRows; r++ )
        for( c = 0; c < nCols; c++ )
            printf( "%d, ", num[ r ][ c ] );
    printf( "\n" );

    return 0;
}

Output

Version 1:
1, 2,
3, 4,
5, 6,

Version 2:
1, 2, 3, 4, 5, 6,

Others will soon comment that the correct definition would be size_t nRows.... One step at a time...

Fe2O30
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