How to write a recursive function?

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How to write a recursive function?

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#1 by (4 votes)
#2 by (4 votes)

3

I was given the task of making this function recursive, but I have no idea how to do it.

int existe (int x){
    FILE *arq;
    int y;
    char buf[MAX];
    arq = fopen ("cliente.txt","r"); 
    fgets (buf,MAX,arq);
    while (!feof(arq)){
          y = atoi(strtok(buf,";"));
          if (x==y){
            fclose (arq);
            return 1;      
          }

        fgets (buf,MAX,arq);
    }
    fclose (arq);
    return 0;

c arquivo

asked by anonymous 29.11.2015 / 21:13

2 answers

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score 4 · Answer 1

What is repeated in the function is the cycle while

    while(!feof(arq)) {
        y = atoi(strtok(buf, ";"));
        if (x == y) {
            fclose(arq);
            return 1;
        }
        fgets(buf, MAX, arq);
    }

So it is with slight changes that you need to replace

int existe(int x) {
    FILE *arq;
    arq = fopen("cliente.txt", "r");

    int value = existe_rec(x, arq);

    fclose(arq);
    return value;
}

int existe_rec(int x, FILE *arq) {
    char buf[MAX];
    if (!fgets(buf, sizeof buf, arq)) return 0;
    if (atoi(buf) == x) return 1; // strtok nao é necessário
    return existe_rec(x, arq);
}

NB: error validation is missing (which was not present in the original version)!

score 4 · Answer 2

Instead of offering ready-made source code, which does not help at all if you need to write new recursive functions in the future, I'll give you tips on how to implement a recursive function .

Any recursive function has the 4 parts below, implemented in this order:

A decision to continue or stop execution based on a control data, evaluated through a conditional expression. The control data is usually passed to the function as a parameter;

A body , where the work is done.

One way to change the control data: : Sometimes changing a counter, or more often by changing which node of the structure is current ;

A way to reverse the execution flow to go back to the beginning: achieved by invoking the function itself again.

For example, the following function prints on the screen (recursively) values from N to 1 :

void countdown(int N)
{
    // 1 - Decisão para parar/continuar
    if (N < 1)
        return;

    // 2 - Corpo
    printf(“%d\n”, N);

    // 3 - Alterar o dado de controle
    N--;

    // 4 - Retrocesso no fluxo de execução
    countdown(N);    
}