Does Declaring Variables Inside a C Loop Impact Performance?

Loop Variable Overhead in C

The question arises whether declaring a variable within a loop incurs any performance penalty. Specifically, consider the following example:

int i = 0;
while (i < 100) {
    int var = 4;
    i++;
}

In this example, the variable var is declared inside the loop body, and it is recreated on each iteration. One might suspect that this repetitive declaration might introduce overhead.

However, in C , stack space for local variables is typically allocated in the function scope. This means that no stack pointer adjustment occurs within the loop; instead, only the value of var is assigned to 4 on each iteration. Consequently, the overhead of declaring the variable within the loop is negligible, and it is equivalent to declaring the variable outside the loop:

int i = 0;
int var;
while (i < 100) {
    var = 4;
    i++;
}

In terms of speed and efficiency, both approaches are essentially identical.

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