Problems with If Else statement chained in C language
I'm starting in programming and had a lot of difficulty understanding if Else in a chained way. I came across the following situation, when running the code only the first or second condition (If/Else) are possible to be true, regardless of the value
float Peso, Altura, Imc;
printf("----------- #17 -----------\n\n");
printf("Para fazer o calculo do IMC, forneca seu peso: \n");
scanf("%f", &Peso);
printf("E sua altura? \n");
scanf("%f", &Altura);
printf("Seu peso e sua altura sao: %.2fKg, %.2fm\n\n",Peso, Altura);
Imc = Peso/(Altura*Altura);
printf("Seu IMC e: %.2f\n", Imc);
if (Imc>=40.0)
{
printf("------------------------------\n");
printf("Voce esta com Obesidade Grau III (morbida)\n");
printf("------------------------------\n");
}
else
{
if(35.0<Imc<39.9)
{
printf("------------------------------\n");
printf("Voce esta com Obesidade Grau II(severa)\n");
printf("------------------------------\n");
}
else
{
if(30.0<Imc<34.9)
{
printf("------------------------------\n");
printf("Voce esta com Obesidade Grau I\n");
printf("------------------------------\n");
}
else
{
if(25.0<Imc<29.9)
{
printf("------------------------------\n");
printf("Voce esta com excesso de peso\n");
printf("------------------------------\n");
}
else
{
if(18.6<Imc<24.9)
{
printf("------------------------------\n");
printf("Voce esta saudavel\n");
printf("------------------------------\n");
}
else
{
if(Imc<18.5)
{
printf("------------------------------\n");
printf("Voce esta abaixo do peso \n");
printf("------------------------------\n");
}
}
}
}
}
}
return 0;
2 answers
If you debug the program you will check that if(30.0<Imc<34.9) is always true, that is, it is not that way you will have to do it.
In C you have to make the comparison this way:
if(Imc<34.9 && 30.0<Imc)
I.e. Imc must be less than 34,9 E Imc it has to be greater than 30.0.
You have to edit all if's and put that way.
Do not confuse && with ||(OU) if you do if(Imc<34.9 || 30.0<Imc)
Means that Imc must be less than 34.9 or Imc greater than 30.0
If Imc=5 the condition is true because only one of them is true, in this case 5<34.9 is true
(@hkotsubo) just to supplement, the operator < returns the value 1 if the comparison is true, and 0 if it is false (see definition here). Therefore, 25.0 < Imc < 29.9 is interpreted as " is the value of the expression 25.0 < Imc less than 29.9?". Since the expression 25.0 < Imc can return only 1 or zero, it will always be less than 29.9, so the expression will always be true.
Let's rearrange and simplify this code using the wonderful if else:
float Peso, Altura, Imc;
printf("----------- #17 -----------\n\n");
printf("Para fazer o calculo do IMC, forneca seu peso: \n");
scanf("%f", &Peso);
printf("E sua altura? \n");
scanf("%f", &Altura);
printf("Seu peso e sua altura sao: %.2fKg, %.2fm\n\n",Peso, Altura);
Imc = Peso / (Altura * Altura);
printf("Seu IMC e: %.2f\n", Imc);
printf("------------------------------\n");
if (Imc >= 40) {
printf("Voce esta com Obesidade Grau III (morbida)\n");
} else if (35 <= Imc && Imc < 40) {
printf("Voce esta com Obesidade Grau II (severa)\n");
} else if (30 <= Imc && Imc < 35) {
printf("Voce esta com Obesidade Grau I\n");
} else if (25 <= Imc && Imc < 30) {
printf("Voce esta com excesso de peso\n");
} else if (18.5 <= Imc && Imc < 25) {
printf("Voce esta saudavel\n");
} else if (Imc < 18.5) {
printf("Voce esta abaixo do peso\n");
}
printf("------------------------------\n");
return 0;
Note that expressions are of type (25 <= Imc && Imc < 30). This is quite different from (25.0<Imc<29.9). Remember someone may have a BMI such as 29.95, so it is important you pay attention where you use the <, <=, >and >= to leave no gap in the conditions however small.
You can still simplify a little more:
if (Imc >= 40) {
printf("Voce esta com Obesidade Grau III (morbida)\n");
} else if (Imc >= 35) {
printf("Voce esta com Obesidade Grau II (severa)\n");
} else if (Imc >= 30) {
printf("Voce esta com Obesidade Grau I\n");
} else if (Imc >= 25) {
printf("Voce esta com excesso de peso\n");
} else if (Imc >= 18.5) {
printf("Voce esta saudavel\n");
} else {
printf("Voce esta abaixo do peso\n");
}
For you can take advantage of the fact that the conditions of the previous ifs do not need to be retested in the subsequent ones. For example, if the test of Imc >= 40 failed and fell on else, then it is obvious that Imc < 40 will always be true in this case and so it does not even need to be tested.