Doubt about switch

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1

I would like the switch show me the sum if I choose case 1 as follows the code, but it does not perform the operations.

#include<stdio.h>

int main() {

int a,b;
int operacao;
int soma = a + b;
int subtracao = a - b;
int multiplicacao = a * b;
int divisao = a / b;
//exponenciacao;


printf("digite o primeiro numero:\n");
scanf("%d", &a);
printf("digite o segundo numero:\n");
scanf("%d", &b);

printf("Qual operacao voce deseja ?\n");
printf(" 1 Soma\n 2 Subtracao\n 3 Multiplicacao\n 4 Divisao\n");
scanf("%d", &operacao);

switch(operacao)
{
case 1:
    printf("voce escolheu soma %d", soma);  *// AQUI EU GOSTARIA QUE ELE REALIZASSE A SOMA, PORÉM ELE SEMPRE APRESENTA O VALOR 10557854* 
    break;
case 2:
    printf("voce escolheu Subtracao %d", subtracao);
    break;
case 3:
    printf("voce escolheu Multiplicacao %d", multiplicacao);
    break;
case 4:
    printf("voce escolheu Divisao %d", divisao);
    break;

}
}
c switch flow-control

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2 answers

4

I don’t know why you created these variables, especially doing the operations before having the values typed. A program executes in an order. And contrary to what you must have learned, you declare the variables as needed, in the location closest to their use.

#include<stdio.h>

int main() {
    int a, b, operacao;
    printf("digite o primeiro numero:\n");
    scanf("%d", &a);
    printf("digite o segundo numero:\n");
    scanf("%d", &b);
    printf("Qual operacao voce deseja ?\n");
    printf(" 1 Soma\n 2 Subtracao\n 3 Multiplicacao\n 4 Divisao\n");
    scanf("%d", &operacao);
    switch (operacao) {
    case 1:
        printf("voce escolheu soma %d", a + b);
        break;
    case 2:
        printf("voce escolheu Subtracao %d", a - b);
        break;
    case 3:
        printf("voce escolheu Multiplicacao %d", a * b);
        break;
    case 4:
        printf("voce escolheu Divisao %d", a / b);
        break;
    }
}

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

3

Operations must be done after you receive the values of the variables.

case 1:
    printf("voce escolheu soma %d", a + b);
    break;

Or

case 1:
    soma = a + b;
    printf("voce escolheu soma %d", soma);
    break;

Your mistake is to perform the sum before having the values of a and b.

  • In case then I always have to call the operation within each case ? because above in the code there is a part that asks the user to enter the values of a and b and the same are assigned to the due variables and in the declension of the variable sum I have already determined that it receives the value of a + b, so I understood then I must "repeat" this declaration process within each case, correct ?

  • 2

    It doesn’t have to be inside the case, but when performing the operation the variables have to have values. if you do so: int a = 10; int b= 20; int sum a +b; // will give 30 But if you do: int a; int b; int sum a +b; // will give problem, the program does not know the values of a and b, How will he add up values he still doesn’t know about? When the program passes through a line it executes the operation.

  • Now I get it man, I forgot the basics of it read the instructions sequentially, thank you so much for the help.

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