Conditions

Decision Making

In life, we all have to make decisions. In order to make a decision we weigh out our options and so do our programs.

Here is the general form of the decision making structures found in C.

int target = 10;
if (target == 10) {
    printf("Target is equal to 10");
}

The if statement

The if statement allows us to check if an expression is true or false, and execute different code according to the result.

To evaluate whether two variables are equal, the == operator is used, just like in the first example.

Inequality operators can also be used to evaluate expressions. For example:

int foo = 1;
int bar = 2;

if (foo < bar) {
    printf("foo is smaller than bar.");
}

if (foo > bar) {
    printf("foo is greater than bar.");
}

We can use the else keyword to exectue code when our expression evaluates to false.

int foo = 1;
int bar = 2;

if (foo < bar) {
    printf("foo is smaller than bar.");
} else {
    printf("foo is greater than bar.");
}

Sometimes we will have more than two outcomes to choose from. In these cases, we can "chain" multiple if else statements together.

int foo = 1;
int bar = 2;

if (foo < bar) {
    printf("foo is smaller than bar.");
} else if (foo == bar) {
    printf("foo is equal to bar.");
} else {
    printf("foo is greater than bar.");
}

You can also nest if else statements if you like.

int peanuts_eaten = 22;
int peanuts_in_jar = 100;
int max_peanut_limit = 50;

if (peanuts_in_jar > 80) {
    if (peanuts_eaten < max_peanut_limit) {
        printf("Take as many peanuts as you want!\n");
    }
} else {
    if (peanuts_eaten > peanuts_in_jar) {
        printf("You can't have anymore peanuts!\n");
    }
    else {
        printf("Alright, just one more peanut.\n");
    }
}

Two or more expressions can be evaluated together using logical operators to check if two expressions evaluate to true together, or at least one of them. To check if two expressions both evaluate to true, use the AND operator &&. To check if at least one of the expressions evaluate to true, use the OR operator ||.

int foo = 1;
int bar = 2;
int moo = 3;

if (foo < bar && moo > bar) {
    printf("foo is smaller than bar AND moo is larger than bar.");
}

if (foo < bar || moo > bar) {
    printf("foo is smaller than bar OR moo is larger than bar.");
}

The NOT operator ! can also be used likewise:

int target = 9;
if (target != 10) {
    printf("Target is not equal to 10");
}

Exercise

In this exercise, you must construct an if statement inside the guessNumber function statement that checks if the number guess is equal to 555. If that is the case, the function must print out using printf "Correct. You guessed it!". If guess is less than 555, the function must print out using printf "Your guess is too low." If guess is greater than 555, the function must print out using printf "Your guess is too high."