Divide vector according to delimiters and copy content to other strings in C

Question

I need the main string "vector" to be traversed to the delimiter '=' and copy the values before '=' to "second" and the values after '=' to "third". I’m sure there’s a smarter way to do this, but as a beginner, I’m having a hard time thinking about the right code for this requirement.

int tam = 256;

char vetor[tam];
char segundo[tam];
char terceiro[tam];
int i = 0;
int j = 0;

fgets(vetor, tam, stdin);

for (i = 0; i < strlen(vetor); i++){
    if (vetor[i] == '='){
        segundo[i] = vetor[i];
    } //continuar percorrendo a string e copiar valores após o delimitador '=' para o vetor "terceiro"
}

The intention is that when the expression is inserted for example: 9+8i*8-3i= it is possible to treat it in different vectors as follows: vector 1: 9 vector 2: +8i vector 3: *8 vector 4: -3i

If there are better ideas for calculating an expression with complex numbers, I am open to ideas =) Ps.1: I try to make the most of C’s native functions, trying to make the most of the external library functions.

Answer 1

One possibility would be:

#include<stdio.h>
#include<string.h>

int main(){

    int tam = 256;
    char vetor[tam];
    char segundo[tam];
    char terceiro[tam];
    int i = 0;
    int j = 0;

    fgets(vetor, tam, stdin);

    for (i = 0; i < strlen(vetor); i++){
        if (vetor[i] != '='){
            segundo[i] = vetor[i];  // Copia apenas caracteres diferentes de '='
        }
        else{
            break;      // Para o loop caso seja encontrado um '='
        }
    }
    segundo[i] = '\0';  // Coloca o término de string (só pra garantir)

    // Aqui o '=' está na posição i, então temos que começar lendo de i+1

    for (j = i+1; j < strlen(vetor); j++){
        if (vetor[j] != '\0'){
            terceiro[j - i- 1] = vetor[j];
        }
        else{
            break;      // Para o loop caso a string acabe (chegue no '\0')
        }
    }
    terceiro[j - i - 1] = '\0';  // Coloca o término de string (só pra garantir)

    printf("segundo = %s\n", segundo);
    printf("terceiro = %s\n", terceiro);

}

Remembering that if the vector string does not have a '=' in the middle the program will not work properly.

Answer 2

How about using the function strtok() of the standard library string.h?

Follow (tested) example of a code similar to yours:

#include <string.h>
#include <stdio.h>

#define MAX_TAM   (256)

int main( void )
{
    FILE * pf = NULL;
    char * p = NULL;
    char vet[ MAX_TAM + 1 ] = {0};
    char segundo[ MAX_TAM + 1 ] = {0};
    char terceiro[ MAX_TAM + 1 ] = {0};

    pf = fopen( "input.txt", "r" );

    if(!pf)
    {
        fprintf( stderr, "Erro ao abrir arquivo de entrada.\n");
        return 1;
    }

    while( fgets( vet, MAX_TAM, pf ) )
    {
        vet[ strcspn( vet, "\n" ) ] = 0;

        p = strtok( vet, "=" );

        if( p )
        {
            strncpy( segundo, p, MAX_TAM );
            p = strtok( NULL, "=" );
            strncpy( terceiro, p, MAX_TAM );

            printf("segundo='%s' terceiro='%s'\n", segundo, terceiro );
        }
    }

    fclose(pf);

    return 0;
}

Entree:

fibo=1.6180
e=2.7182
pi=3.1415
sqrt2=1.4142
sqrt3=1.7320

Exit:

segundo='fibo' terceiro='1.6180'
segundo='e' terceiro='2.7182'
segundo='pi' terceiro='3.1415'
segundo='sqrt2' terceiro='1.4142'
segundo='sqrt3' terceiro='1.7320'

I hope I’ve helped!