#include <stdio.h>

typedef void *(*TSeqPtr)(void);

int seq_sum;
int seq_i;

void *SeqA(void);
void *SeqB(void);
void *SeqC(void);

void *SeqA(void)
{
    seq_sum = 0;
    seq_i = 0;
    printf("初期化 : %d\n", seq_sum);
    return SeqB;
}

void *SeqB(void)
{
    seq_i++;
    seq_sum += seq_i;
    printf("処理 : %d\n", seq_i);
    return (seq_i < 10) ? SeqB : SeqC;
}

void *SeqC(void)
{
    printf("結果 : %d\n", seq_sum);
    return NULL;
}

void main(void)
{
    TSeqPtr seq = SeqA;
    do {
        seq = (TSeqPtr)seq();
    } while ( seq != NULL );
}

void A(int *v,int *n){
    *n = 0;
    *v = 0;
    printf("初期化 : %d\n", *v);
}

void B(int *v ,int *n){
    (*v)++;
    *n += *v;
    printf("処理 : %d\n", *v);
}
void C(const int* n){
    printf("結果 : %d\n", *n);
}
void all_func(int val){
    int sum,plus;
    A(&plus,&sum);
    while(1){
        if(plus < val) B(&plus,&sum);
        else{ C(&sum);break;}

    }
}
typedef void (*AllFuncType)(int);
AllFuncType AllFunc(void){
    return all_func;
}
int main(void){
    all_func(10);
    AllFunc()(20);
    return 0;
}

#include <stdio.h>

typedef struct TSeq { struct TSeq (*f)(void); } TSeq;

int seq_sum;
int seq_i;

TSeq SeqA(void);
TSeq SeqB(void);
TSeq SeqC(void);

TSeq tseq[] = { NULL, SeqA, SeqB, SeqC };

TSeq SeqA(void)
{
    seq_sum = 0;
    seq_i = 0;
    printf("初期化 : %d\n", seq_sum);
    return tseq[2];
}

TSeq SeqB(void)
{
    seq_i++;
    seq_sum += seq_i;
    printf("処理 : %d\n", seq_i);
    return (seq_i < 10) ? tseq[2] : tseq[3];
}

TSeq SeqC(void)
{
    printf("結果 : %d\n", seq_sum);
    return tseq[0];
}

int main(void)
{
    TSeq seq = tseq[1];

    do {
        seq = seq.f();
    } while (seq.f != NULL);
    return 0;
}

TSeq tseq[] = { NULL, SeqA, SeqB, SeqC }; の代わりに、

TSeq seq0 = { NULL };
TSeq seqA = { SeqA };
TSeq seqB = { SeqB };
TSeq seqC = { SeqC };

とすれば、return tseq[2]; を return seqB; と書けます。

struct T;
struct T f(void);
struct T (*pf)(void);

int main(void) { return 0; }