CODEWITHSUNDEEP
cmultidimensional-array
Rivf
Rivf

Reputation: 125

Traversing Two Dimensional Array

How come Line 1 and Line 2 have more than ten x(s) when the loop should end at ten given the condition of ii < 10?

I am trying to understand how these two dimensional arrays work, any advice is appreciated.

#include <stdio.h>
int main()
{
    char name[3][10];

    for(int i = 0; i < 3; i++){
        for(int ii = 0; ii < 10; ii++){
            name[i][ii] = 'x';
        }
    }


    printf("Line 1: %s.\n", name[0]);

    printf("Line 2: %s.\n", name[1]);

    printf("Line 3: %s.\n", name[2]);


    return 0;
}

FIX:

Thanks to everyone's comments I managed to fix the code. The problem was that I was not reserving one space for the NULL terminator at the end of the array. Since I wanted ten x(s), the solution is to increase the size of the two dimensional array so that it has space for the NULL terminators.

#include <stdio.h>
int main()
{
    char name[4][11];

    for(int i = 0; i < 3; i++){
        for(int ii = 0; ii < 10; ii++){
            name[i][ii] = 'x';
        }
    }


    printf("Line 1: %s.\n", name[0]);

    printf("Line 2: %s.\n", name[1]);

    printf("Line 3: %s.\n", name[2]);


    return 0;
}

Upvotes: 1

Views: 92

Answers (1)

4386427
4386427

Reputation: 44274

As it has been discussed in comments, the problem with your code was that you didn't add a NUL to terminate the strings.

However, I'll post an answer as your fix isn't really a fix

Two things to mention:

  1. You don't need to extend the dimension of the array to [4][11] but only to [3][11]. It's only the number of chars in each string that need to be increased to make room for the termination. Changing [3] will give you room for an extra string and that is not what you are looking for. So use [3][11]

  2. Your fix still doesn't add the NUL terminator. Remember that a local variable isn't automatic initialized so you need to do it yourself. In other words - you need some code that explicit sets name[i][10] to NUL.

This is how memory is looking in your original code, your fix and how you really want it.

enter image description here

Below is two ways to get what you want.

Option 1:

char name[3][11];

for(int i = 0; i < 3; i++){
    for(int ii = 0; ii < 10; ii++){
        name[i][ii] = 'x';
    }

    // Add NUL to the end to get a correct C style string
    name[i][ii] = '\0';
}

Option 2:

// Explicit initialize the whole array to zero
char name[3][11] = { 0 };

for(int i = 0; i < 3; i++){
    for(int ii = 0; ii < 10; ii++){
        name[i][ii] = 'x';
    }
}

I prefer option 1 but option 2 will also do the job.

Upvotes: 3

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