[__]

pawn Код:

stock countTabulatedOccurrences(string[]) {
    new
        tCount;
        
    for(new it = 0; it < strlen(string); it++) {
        if(string[it] == '\t') tCount++;
    }
    
    return tCount;
}

Tested and works.

'\t' is not a string, it is just a single character due to the slash making it a control character.