The goto is a non-conditional jump, can be considered the basis for all flow control .
With a combination of if and goto you can create any flow control, I think this is the purpose of the peculiar exercise.
Although your code is already reduced to if s. I recommend that you write the normal way code and then replace the flow controls by constructions using goto (if not resolved), as in the examples:
if / else
if(x==0)
{
printf("verdadeiro\n");
}
else
{
printf("falso\n");
}
printf("fim if else\n");
Can be represented with goto s:
if(x==0)
goto if_1; //se o if for verdadeiro, executa essa expressão
goto else_1; //se for falso, ignora a expressão anterior e executa essa
if_1:
printf("verdadeiro\n");
goto fim_if_else1;
else_1:
printf("falso\n");
goto fim_if_else1;
fim_if_else_1:
printf("fim if else\n");
for
Data:
int a=0;
int b=5;
int x;
The loop:
for(x=a; x<b; x++)
{
printf("{for entre [%d e %d)} x = %d, \n", a, b, x);
}
printf("fim [for]\n");
Can be made explicit using goto s:
inicio_for_1:
x=0;
verifica_for_1:
if(x<b)
goto corpo_for_1;
goto fim_for_1;
corpo_for_1:
printf("{for entre [%d e %d)} x = %d, \n", a, b, x);
incremento_for_1:
x++;
goto verifica_for_1;
fim_for_1:
printf("fim [for]\n");
do ... while
The code
int x = 5;
do
{
x--;
printf("%d\n", x);
}
while(x>0);
printf("fim do{...}while(...)\n");
can be represented as:
inicio_dowhile_1:
int x=5;
corpo_dowhile_1:
x--;
printf("%d\n", x);
verifica_dowhile_1:
if(x>0)
goto corpo_dowhile_1;
fim_dowhile_1:
printf("fim do{...}while(...)\n");
Function call
C requires the main function, where the program starts. Other functions can be encoded within this, and arguments can be declared as local variables. You will be emulating a function call and parameter passing:
int func1(int x, int y)
{
return x*y;
}
int main(void)
{
int r = func1(4,5);
printf("%d", r);
}
It can be represented like this:
int main(void)
{
//espaço para declarar todas variáveis necessárias
int func1_argx;
int func1_argy;
int func1_resultado;
int r;
//equivalente a chamar função:
func1_argx = 4; //define primeiro argumento
func1_argy = 5; //define segundo argumento
goto func1_interna; //~chama função~
ponto_retorno: //nomeia ponto de retorno
//resto do código da main
r = func1_resultado;
printf("%d", r);
goto main_final; //vai para o final do main, ignorando código da função
//parte reservada para função:
func1_interna:
func1_resultado = func1_argx*func1_argy;
goto ponto_retorno;
main_final: ;
}
In addition to replacing flow controllers, you can make a code as complex and confusing as you like, giving rise to what is called spaghetti code , but I do not think your teacher is looking for something like this ...
This answer has didactic purposes, try to understand the equivalence of constructions =)
Maybe your course will go to low-level languages later ... At the hardware level the execution controls are implemented by tests on registers and jumps, something directly related to if s and goto s.
