What Happens if the Conditional Expression is Missing in an if Statement in C?

In C, the if statement needs a conditional expression to decide whether to execute a block of code. This condition is usually a logical or relational expression that returns either true (non-zero) or false (zero).

Syntax of a valid if statement:

if (condition)
{
    // code to execute if condition is true
}

What If the Condition Is Missing?

If the conditional expression is missing, the C compiler will throw a syntax error. This is because the if statement needs a valid expression to evaluate.

Example – Compilation Error:

#include <stdio.h>
 
int main()
{
    if ()  // Missing condition
    {  
        printf("This will cause a compiler error.\n");
    }
    return 0;
}

Error Message:

error: expected expression before ')' token

Correct Example with a Condition:

#include <stdio.h>
 
int main()
{
    if (1) // Condition present, evaluates to true
    {
        printf("This will execute because the condition is true.\n");
    }
    return 0;
}

You can use any valid expression that evaluates to non-zero (true) or zero (false). Even a constant like 1 (true) or 0 (false) works.

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