Arrays are not storing values in the loop

Question

That's my C code. I'm trying to store values in my arrays using the for-loop but nothing is stored and only the value of the variable trackingCodes changes. I don't where the errors comes from . No compiling errors

#include <stdio.h>

int main(void) {
int trackingCodes = 0;
char typeCode[trackingCodes];
int codeLength [trackingCodes];
int byteChar = 0;
int byteInt = 0;
int byteDouble = 0;
int j = 0;
int totalBytes = 0;
int totalByteDouble = 0;
int totalByteInt = 0;
int totalByteChar = 0;


scanf("%d", &trackingCodes);

for ( j = 0; j < trackingCodes; j++)
{
    scanf("%d %c", &codeLength[j], &typeCode[j]);
    if (typeCode[j] == 'c')
    {
        byteChar = codeLength[j] * sizeof(char);
        totalByteChar = totalByteChar + byteChar;

    }
     else if (typeCode[j] == 'i')
    {
        byteInt = codeLength[j] * sizeof(int);
        totalByteInt = totalByteInt + byteInt;

    }
     else if (typeCode[j] == 'd')
    {
        byteDouble = codeLength[j] * sizeof(double);
        totalByteDouble = totalByteDouble + byteDouble;

    } 

}

    totalBytes = totalByteChar + totalByteDouble + totalByteInt;
    int t = 0;

    for(t = 0; t < trackingCodes; t++){
        if(codeLength[t] != 'i' && codeLength[t] != 'c' && codeLength[t] != 'd'){
            printf("Invalid Tracking code type");
            return 0;
        }
    }

    printf("%d bytes\n", totalBytes);



    return 0;
}```

Answer 1

You need to move the array definition so that it is after you have read trackingCodes . In this way you create a Variable Length Array with the size scanned. Like:

scanf("%d", &trackingCodes);

char typeCode[trackingCodes];
int codeLength [trackingCodes];

And... Always check the return value from scanf - that is:

if (scanf("%d", &trackingCodes) != 1)
{
    // error handling
}

Answer 2

I think you think the code:

int trackingCodes = 0;
char typeCode[trackingCode];

Will indefinitely bind the size of typeCode to the value of trackingCodes . It's actually going to declare typeCode with the size of the current value of trackingCodes .

Solutions are to either scan your input from stdin as covered in @4386427's answer, or to allocate it with dynamic memory management ( malloc / free and co.)