Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Is a For Loop always executed at least once?
Ask Question. Asked 4 years, 4 months ago. Active 2 years, 8 months ago. Viewed 28k times. Edit : Thanks for all those quick answers, I guess this case is already closed.
Klaus Klaus 1 1 gold badge 1 1 silver badge 5 5 bronze badges. A for loop won't execute at all if the condition is false before the first iteration. Your teacher's statement is complete and utter nonsense, as your test easily demonstrates. BaummitAugen OP is right in doing research beyond testing himself. According to my teacher, a for-loop always executes at least once, even if the condition is not met.
According to her, this loop would execute at least once, yet it does not, or am I missing something? Is there any case, no matter what language, where this would execute once?
To eliminate the thought in advance: yes, it was about for loops, not do-while-loops. A loop will only execute while its condition is true. It is also called an exit-controlled loop. As we saw in a while loop, the body is executed if and only if the condition is true.
In some cases, we have to execute a body of the loop at least once even if the condition is false. This type of operation can be achieved by using a do-while loop. In the do-while loop, the body of a loop is always executed at least once. After the body is executed, then it checks the condition. If the condition is true, then it will again execute the body of a loop otherwise control is transferred out of the loop.
Similar to the while loop, once the control goes out of the loop the statements which are immediately after the loop is executed. The critical difference between the while and do-while loop is that in while loop the while is written at the beginning. In do-while loop, the while condition is written at the end and terminates with a semi-colon ;.
In the above example, we have printed multiplication table of 2 using a do-while loop. The general structure of for loop syntax in C is as follows:. Notice that loops can also be nested where there is an outer loop and an inner loop.
For each iteration of the outer loop, the inner loop repeats its entire cycle. Consider the following example with multiple conditions in for loop, that uses nested for loop in C programming to output a multiplication table:. The nesting of for loops can be done up-to any level. The nested loops should be adequately indented to make code readable.
We will expand on this later in the course to deal with a few more obscure ways the user can go wrong entering numbers. The text of each key point is a link to the place in the web page.
The while loop The while loop repeats as long as the condition is true non-zero. The increment Understanding the increment is critical to understanding the loop. Key example: The while loop Debugging loops Mentally check how a loop starts Mentally check how a loop increments and finishes. On this page. The while loop.
Loops: while , for and do.. Mini-exercise NB: if you have problems with this see the min-exercise in the section "Debugging loops". Example: a power function We can use the while loop to write a "poor man's power function" which calculates value to the power of exponent where exponent is a positive integer. To observe the behavious of the increment.
Step through the above "Key example" in a new window. Step through the code observing the change in the value of exponent. If you don't get it right first time, refresh the page and try again until you do. Debugging loops Loops can easily go wrong with the most common problems being: Loops that never start. Loops that never finish.
Loops that repeat the wrong number of times. Check how a loop starts When examining any loop it's good to ask "what would happen if the condition were false the very first time it was evaluated? Mentally check how a loop starts Check how a loop increments and finishes. A description of what it is: simply printing out anonymous numbers is extremely confusing. Another extremely useful tactic is to print out the "input" values at the start of the loop and the result at the end, Add some debugging output to your previous loop To demonstrate some debugging.
After your call to scanf in the loop add a call to printf to print out the value you have just read in. Make sure the printf statement also has some helpful text so it's not just an anonymous number. Execute the body of the calculation. This Initialise, Test, Increment loop is so common that it has a loop especially for it, the for loop: The for loop The for loop rolls all these three into one. Execute the body.
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