There is a sentence about "statement" that I can't understand in C Primer Plus by Stephen Prata -

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• expression versus statement 18 answers

there sentence "statement" can't understand in c primer plus stephen prata.

in chapter 5, there section explains difference between statement , expression. author explains statement follows:

statements

statements primary building blocks of program. program series of statements necessary punctuation. statement complete instruction computer. in c, statements indicated semicolon @ end. therefore,

legs = 4 is expression (which part of larger expression), but legs = 4;

is statement.

and author gives example:

although statement (or, @ least, sensible statement) complete instruction, not complete instructions statements. consider following statement:

x = 6 + (y = 5);

in it, subexpression y = 5 complete instruction, part of statement. because complete instruction not statement, semicolon needed identify instructions statements.

the authors says "y=5"is complete instruction mentioned above isn't expression, not complete statement?

every c program comprises of statements. program executes statement statement. each statement generally, in turn, comprises of expression. , expression may further comprise of sub-expressions. example:

/* diff_statements.c */ #include <stdio.h> #define size 10        /* size symbolic constant */   int main(void) {     int index, sum;    /* declaration statement */     int boys[size];    /* array declaration */      printf("user enter no of boys in 10 classes...\n");     /* function statement */      (index = 0; index < size; index++)          scanf("%d", &boys[index]);      /* statement single statement */       /* it's practice review if u entered correct values */      printf("no. of boys entered 10 classes as:\n");     (index = 0; index < size; index++)         printf("%d\t", boys[index]);     printf("\n");      printf("summing & displaying boys in classes...\n");      /* statement block of statements */          (index = 0; index < size; index++) {         sum += boys[index];         ;   /* null statement; nothing here */     }      printf("total boys in %d classes %d\n", size, sum);     return 0; } 

every c statement ends semicolon ‘;’. while expressions don’t. example:

x + y;    /* x + y exp x + y; statement. */ 5 + 7;    /* above */  while (5 < 10) {       /* 5 < 10 relational exp, not statement. */     /* used while test condition */      /* other statements in while loop */ }  result = (float) (x * y) / (u + v);  okey = (x * y) / (u + w) * (z = + b + c + d);  /* (z = + b + c + d) sub-expression in above */ /* expression. */ 

expressions complete instruction in human logic, not according c. point of view of c, complete instruction statement, valid combination of expressions ended semi-colon.