Editing BASIC (section)

==== Program flow control ====
; <code>IF ... THEN ... {ELSE}</code> : used to perform comparisons or make decisions. Early dialects only allowed a line number after the <code>THEN</code>, but later versions allowed any valid statement to follow. <code>ELSE</code> was not widely supported, especially in earlier versions.
; <code>FOR ... TO ... {STEP} ... NEXT</code> : repeat a section of code a given number of times. A variable that acts as a counter, the "index", is available within the [[Control flow#Loops|loop]].
; <code>WHILE ... WEND</code> and <code>REPEAT ... UNTIL</code> : repeat a section of code while the specified condition is true. The condition may be evaluated before each iteration of the loop, or after. Both of these commands are found mostly in later dialects.
; <code>DO ... LOOP {WHILE}</code> or <code>{UNTIL}</code> : repeat a section of code indefinitely or while/until the specified condition is true. The condition may be evaluated before each iteration of the loop, or after. Similar to <code>WHILE</code>, these keywords are mostly found in later dialects.
; <code>[[Goto|GOTO]]</code> : jumps to a numbered or labelled line in the program. Most dialects also allowed the form {{code|GO TO}}.
; <code>GOSUB ... RETURN</code> : jumps to a numbered or labelled line, executes the code it finds there until it reaches a <code>RETURN</code> command, on which it jumps back to the statement following the <code>GOSUB</code>, either after a colon, or on the next line. This is used to implement [[subroutine]]s.
; <code>ON ... GOTO/GOSUB</code> : chooses where to jump based on the specified conditions. See [[Switch statement]] for other forms.
; <code>DEF FN</code> : a pair of keywords introduced in the early 1960s to define functions. The original BASIC functions were modelled on FORTRAN single-line functions. BASIC functions were one expression with variable arguments, rather than [[subroutine]]s, with a syntax on the model of <code>DEF FND(x) = x*x</code> at the beginning of a program. Function names were originally restricted to FN, plus one letter, ''i.e.'', FNA, FNB&nbsp;...