C programming notes - School of Physics

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C programming notes file:///F:/my_docs/web_phys2020/Cprogrammingnotes.html 22 of 40 19/03/2007 10:06 AM } A related control mechanism is the do-while loop initial_expression; do{statement;} while (loop_condition) For example (dowhile.c): i = 0; do {printf("The value of i is now %d\n", i); i = i + 1; } while (i < 5); Here is a slightly more interesting example which converts Centigrade to Farenheit (tempconv.c). And here is a more complex example, illustrating nested loops, with an if thrown in for good measure: ASCII circle printer. And here is another program illustrating the power of loops: Mandelbrot image generator Semicolons in compound statements The last statement in the body of statements in a "for" loop (or, in fact, in any other compound statement) must be terminated with a semicolon. For example, for (i = 0; i < 10; i++) { x = i * i; x += 2; /* the semicolon is required here */ } /* do not use a semicolon here */ Variables defined within compound statements You can create variables that are local to a compound statement by declaring the variables immediately after the leading curly bracket. If statements if (expression) statement else if (expression) statement else if (expression) statement else statement Where "statement" is a simple C statement ending in a semicolon, or a compound statement ending in a curly bracket. Some examples will help: if (i == 6) x = 3; if (i == 6) { x = 3; } if (i) x = 3; if (i == 2) x = 3; else if (i == 1) if (j) y = 2;
C programming notes file:///F:/my_docs/web_phys2020/Cprogrammingnotes.html 23 of 40 19/03/2007 10:06 AM else /* NOTE: possible ambiguity here, the compiler uses */ y = 3; /* the closest if statement that does not have */ else { /* an else clause */ x = 4; y = 5; } Example Program ifelse.c Break and continue These two statements are used in loop control. "break" exits the innermost current loop. "continue" starts the next iteration of the loop. Here is an examaple program with break and continue (breakcon.c) Infinite loops Here are three ways of writing an infinite loop, choose whichever one you like: for (;;;) { statement; } while (1) { statement; } do { statement; } while (1); Infinite loops can be useful. They are normally terminated using a conditional test with a "break" or "return" statement. For example: while (1) { statement; if (logical_condition) break; } goto C does have a "goto" statement, but you normally don't need it. Using "goto" is usually a result of bad programming (although in some circumstances it can be a sensible choice). The switch statement The switch statement allows you to choose between multiple paths of execution depending on the value of an expression. It could be replaced by a series of if statements, but switch can make the flow of the program easier to understand. switch (expression) { case const-expression: statements case const-expression: statements default: statements } Beware that control will flow from one case to the next unless you explicitly include a break statement to cause control to skip to the end of the switch statement. Here is an example of using switch: switch (i) { case 0: printf("i had the value zero\n"); break; case 1: case 2: printf("i was either one or two\n");
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C programming notes - School of Physics

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