Interlink two strings into one vector

Question

/**
    5. Faça um programa que receba 2 strings (A e B) e 
    retorne uma terceira string (C) formada pelos caracteres de A e B intercalados. 
    Ex.: Se A='Quarta' e B='Segunda', a resposta deve ser 'QSueagrutnada'
**/

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

main(){
    char s1[30], s2[30], s3[60];
    int i=0, tamanho=0;

    printf("String 1: ");
    scanf(" %s", s1);

    printf("String 2: ");
    scanf(" %s", s2);

    tamanho = strlen(s1) + strlen(s2);

    for(i; i < tamanho; i++){
        if(s3[i]%2 == 0){
            s3[i] = s1[i];
        }else{
            s3[i] = s2[i];
        }
    }

    printf(" %s", s3);
}

The pro result I’ve done so far is this, I thought - I’ll concatenate a letter in the even position and another letter in the odd position but in logic it didn’t look like I imagined

I know in C I learned about function strcat(), but I don’t know how to apply in this example.

Answer 1

Some problems I noticed

1. The comparison s3[i]%2 == 0 is wrong. To know if the position of the resulting string is even or odd do i % 2 == 0
2. s1[i] and s2[i] shouldn’t use i as an index. i is incremented to each loop and represents the index of the resulting string. This means that you will skip a character of each string because of the parity check, generating a wrong result. Instead, keep individual indices for the first and second string.
3. It is necessary to check that the index of the two strings does not exceed their respective sizes.

Considering the points I mentioned above, the changes would leave the code like this:

for (i; i < tamanho; i++) {
    if (i % 2 == 0 && indiceString1 < tamanhoString1) {
        s3[i] = s1[indiceString1++];
    } else if (indiceString2 >= tamanhoString2) {
        s3[i] = s1[indiceString1++];
    }
    else {
        s3[i] = s2[indiceString2++];
    }
}

Online example here.

Answer 2

How about a specific function for your case:

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


char * intercalar( char * s, const char * a, const char * b )
{
    int i = 0;
    int lena = strlen(a);
    int lenb = strlen(b);
    int len = lena + lenb;

    for( i = 0; i < lena; i++ )
        s[ i * 2 ] = a[i];

    for( i = 0; i < lenb; i++ )
        s[ 1 + i * 2 ] = b[i];

    s[ len ] = 0;

    return s;
}


int main( int argc, char ** argv )
{
    char * a = "Quarta";
    char * b = "Segunda";
    char saida[100] = {0};

    intercalar( saida, a, b );

    printf("a = %s\n", a );
    printf("b = %s\n", b );
    printf("saida = %s\n", saida );

    return 0;
}

Testing:

$ ./intercalar 
a = Quarta
b = Segunda
saida = QSueagrutnad

Answer 3

Observing the care that the @Maniero quoted and its related links, as well as the observations of reply from @mercador, I decided to put a pointer-based response.

The idea is to navigate with the pointer itself until you reach the point of the null character. While it is possible to navigate both pointers referring to strings s1 and s2, sail in both. If I reach the null character of one of them, I finish the loop of the double navigation and I navigate in each of them individually. Note that, case s1 has reached its end, a later tie in s1 until the null character does not meet the condition of the while.

void intercala(char *saida, char *s1, char *s2) {
  while (*s1 != '\0' && *s2 != '\0') {
    *saida = *s1;
    saida++;
    *saida = *s2;
    saida++;
    s1++;
    s2++;
  }
  while (*s1 != '\0') {
    *saida = *s1;
    saida++;
    s1++;
  }
  while (*s2 != '\0') {
    *saida = *s2;
    saida++;
    s2++;
  }
}

Answer 4

Oops! the error is in the indexes you are passing in arrays S1 and s2. At each loop a letter is left behind. To fix this you must assign a different index for each variable S1 and s2. Follow the corrected code. I hope to have helped!

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

    main(){
      char s1[30], s2[30], s3[60];
      int i=0,j=0, k=0, tamanho=0;

      printf("String 1: ");
      scanf(" %s", s1);

      printf("String 2: ");
      scanf(" %s", s2);

      tamanho = strlen(s1) + strlen(s2);

      for(i, j, k; i < tamanho; i++){

        if(i%2 == 0){
          s3[i] = s1[j];
          j++;
        }else{
         s3[i] = s2[k];
          k++;
        }
      }
        printf ("%d\n", tamanho);

      printf(" %s", s3);
      return 0;
    }

Answer 5

I’m new at this, mine’s like this:

#inlcude <stdio.h>

int main() {
    char string1[100] ,string2[100];
    int i;

    for(i=0 ; i<100 ; i++){
        string1[i]=0;
        string2[i]=0;
    }
    scanf("%s" ,string1);
    scanf("%s" ,string2);

    for(i=0 ; i<100 ; i++){
        if(string1[i]>=34 && string1[i]<127){
            printf("%c" ,string1[i]);
        }
        if(string2[i]>=34 && string2[i]<127){
            printf("%c" ,string2[i]);
        }

    }


  return 0;
}

Answer 6

I couldn’t test it, but probably this way it works:

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

void main(){
    char s1[30], s2[30], s3[60];
    int i=0, tamanho=0, indexS1 = 0, indexS2 = 0;

    printf("String 1: ");
    scanf(" %s", s1);

    printf("String 2: ");
    scanf(" %s", s2);

    tamanho = strlen(s1) + strlen(s2);

    for(i; i < tamanho; i++){
    if ((i < strlen(s1)) && (i < strlen(s2))) {
        if((i % 2) == 0){
            s3[i] = s1[indexS1];
            indexS1++;
        }else{
            s3[i] = s2[indexS2];
            indexS2++;
        }
    } else if (i < strlen(s1)) {
        s3[i] = s1[indexS1];
        indexS1++;
    } else if (i < strlen(s2)) {
        s3[i] = s2[indexS2];
        indexS2++;
    }
}

    printf(" %s", s3);
}