Passing vector to functions

Question

How do I pass a vector to a function? Something that, on the Moon, would be like this:

vector = {"V", "e", "t", "o", "r"}
function getVector(vector, pos)
    return vector[pos]
end
print(getVector(vector, 1))
Output: "V"

I tried so:

#include <stdio.h>
void main() {
    char vector[5] = {"V", "e", "t", "o", "r"};
    char getVector(char vector[], int pos) {
        return vector[pos];
    }
    printf("%c", getVector(vector, 0));
}

The mistakes:

G:\PROJETOS\C\test.c    In function 'main':
3   5   G:\PROJETOS\C\test.c    [Error] excess elements in char array initializer
3   5   G:\PROJETOS\C\test.c    [Error] (near initialization for 'vector')
3   5   G:\PROJETOS\C\test.c    [Error] excess elements in char array initializer
3   5   G:\PROJETOS\C\test.c    [Error] (near initialization for 'vector')
3   5   G:\PROJETOS\C\test.c    [Error] excess elements in char array initializer
3   5   G:\PROJETOS\C\test.c    [Error] (near initialization for 'vector')
3   5   G:\PROJETOS\C\test.c    [Error] excess elements in char array initializer
3   5   G:\PROJETOS\C\test.c    [Error] (near initialization for 'vector')

Answer 1

The code has some problems:

• The Main() need to return a int. Some compilers accept different from this but it is out of the standard, learn to do everything by default.
• One function cannot be inside the other. And the called function must be declared before its use. Its definition may be later but it’s more practical to do before (next to the statement, so you don’t have to put its header twice) in simple cases like this.
• You declared the vector as type char but put strings inside it as elements. There is a difference between single and double quotes. The character literal is with single quotes.

Code:

#include <stdio.h>

char getVector(char vector[], int pos) {
    return vector[pos];
}

int main() {
    char vector[5] = {'V', 'e', 't', 'o', 'r'};
    printf("%c", getVector(vector, 0));
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

Answer 2

In C you cannot pass vectors by value, only by reference (i.e. you need to pass a pro vector pointer, not the vector itself). However, the C syntax allows you to define your function in this way:

char getVector(char vector[], int pos) {

And the compiler ensures that the vector automatically decays to a pointer. Source.

However, the same is not true for multidimensional vectors:

char vector[5][2] = {"V", "e", "t", "o", "r"};

char getVector(char vector[][], int pos, int pos2) { // Não funciona

char getVector(char vector[][2], int pos, int pos2) { // Funciona

char getVector(char **vector, int pos, int pos2) { // Funciona

Source. Source.

As for your compilation errors:

• In C there is a difference between a string and a single character: strings are bounded by double quotes, and characters by single quotes. So your vector initialization should be:

  char vector[5] = {'V', 'e', 't', 'o', 'r'};
  

• You cannot create functions within other functions in C. Pass your getVector out of function main.

Answer 3

The other answers already solve your problem, but I would like to collaborate.

In Lua there is no difference between "V", 'V' and [[V]], how do you read here. All treated as strings. But in C single quotes and double quotes has different meanings.

In C and C++, single quotes are used for a single character and double quotes for strings. In the case of strings, the compiler includes a character null or '\0', to identify the end of the string.

So that:

char str1[] = "Hello";

It amounts to this, with the '\0' in the end:

char str2[] = { 'H','e','l','l','o','\0' };

Example: ideone